When GOBIN is not set, BIN must be set to the single-path workaround
value of GOPATH, because Circle.

This PR updates GNUMakefile to respect $GOBIN if it is set in the
environment or via an $GOENV file. Previously we hard-coded the output
to $GOPATH/bin, which is not necessarily the desired behavior.

Since switching to `golangci-lint` we have set the `-j 1` flag, which
restricts the tool to using 1 CPU thread.

This PR removes the flag so `make check` takes less time on good
computers.

This PR upgrades our CI images and fixes some affected tests.

- upgrade go-machine-image to premade latest ubuntu LTS (ubuntu-2004:202111-02)

- eliminate go-machine-recent-image (no longer necessary)

- manage GOPATH in GNUMakefile (see https://discuss.circleci.com/t/gopath-is-set-to-multiple-directories/7174)

- fix tcp dial error check (message seems to be OS specific)

- spot check values measured instead of specifically 'RSS' (rss no longer reported in cgroups v2)

- use safe MkdirTemp for generating tmpfiles

NOT applied: (too flakey)

- eliminate setting GOMAXPROCS=1 (build tools were also affected by this setting)

- upgrade resource type for all imanges to large (2C -> 4C)

## Development Environment Changes
* Added stringer to build deps

## New HTTP APIs
* Added scheduler worker config API
* Added scheduler worker info API

## New Internals
* (Scheduler)Worker API refactor—Start(), Stop(), Pause(), Resume()
* Update shutdown to use context
* Add mutex for contended server data
    - `workerLock` for the `workers` slice
    - `workerConfigLock` for the `Server.Config.NumSchedulers` and
      `Server.Config.EnabledSchedulers` values

## Other
* Adding docs for scheduler worker api
* Add changelog message
Co-authored-by: Derek Strickland <1111455+DerekStrickland@users.noreply.github.com>

Meant for development purposes only, so one can compile binary on a
macos host then start a Docker container or scp the binary to a linux
host easily.

The resulting binary is statically linked and has very subtle
differences. e.g. static binaries use go native network stack that
honor /etc/hosts and /etc/resolve differently from the glibc
implementation. In development environment, I don't expect these to
materially change our experience.

* Remove vendor folder during make clean
* Add vendor warning to make dev build command

Also update LAST_RELEASE in makefile to 1.1.5

Also format terraform scripts with hclfmt, equivalent to terraform fmt.

I opted not to use terraform fmt, because I didn't want to introduce dev dependency on the terraform CLI.

Also, I've optimized the find command to ignore spurious directories (e.g. .git, node_modules) that seem to be populated with too many files! make hclfmt takes 0.3s on my mac down from 7 seconds!

This PR removes the vendor directory from the Nomad repository.
Contributers will no longer need to deal with our `make sync`
step when working on Nomad, which was suprising when making changes
to the api. It also causes huge diffs in PRs that nobody looks at.

Adopts [`go-changelog`](https://github.com/hashicorp/go-changelog) for managing Nomad's changelog. `go-changelog` is becoming the HashiCorp defacto standard tool for managing changelog, e.g. [Consul](https://github.com/hashicorp/consul/pull/8387), [Vault](https://github.com/hashicorp/vault/pull/10363), [Waypoint](https://github.com/hashicorp/waypoint/pull/1179). [Consul](https://github.com/hashicorp/consul/pull/8387) seems to be the first product to adopt it, and its PR has the most context - though I've updated `.changelog/README.md` with the relevant info here.

## Changes to developers workflow

When opening PRs, developers should add a changelog entry in `.changelog/<PR#>.txt`. Check [`.changelog/README.md`](https://github.com/hashicorp/nomad/blob/docs-adopt-gochangelog/.changelog/README.md#developer-guide). 

For the WIP release, entries can be amended even after the PR merged, and new files may be added post-hoc (e.g. during transition period, missed accide...

Previously installing buf was left out of `make bootstrap` because it
had conflicts with the `tools/go.mod` file and dependencies used by
other tools. With Go 1.16 we eliminated that `go.mod` file, and can
now just install `buf` with `go install` like everything else.

Signed-off-by: Yoan Blanc <yoan@dosimple.ch>

Only use cross compile if not compiling in target architecture.

Also, use the latest gcc for cross compilation.

This change disables using msgpack generated serializers in dev by
default.

In released binaries, we use code-generated msgpack serializers to
improve performance.  However, in development, code generated
serializers are a pain. If a developer forgets to re-generate code, the
code generated gets out of sync with the go structs, and result into
subtle bugs where some values appear not to persist as expected.

The CI and release scripts will continue to use the msgpack
code-generation. Devs who want to test locally can set
`GO_TAGS=codegen_generated` as well.

Golang 1.16 added better support for installing tools, without updating
go.mod files: https://blog.golang.org/go116-module-changes#TOC_4. .

This is required because Go does not pull CC from the make variable. This uses
whatever Go's default CC unless CC is overridden, as it is for the ARM targets.

This also makes it easier to build Nomad on a native ARM device, via:

```
make CC= pkg/linux_arm/nomad
```

* Set 'only' ALL_TARGETS rather than append

This is functionally no different than before, but it's more correct.

* Re-scope VERBOSE=true

Previously this was only set when the OS was Linux; this was added in
805ade7d.

* Warn about unsupported OS rather than error

Also:

* Only print the warning when trying to build Nomad
* Print correct list of supported OSes

This removes small differences between the targets, like the statement
about what's being built.

The CGO/Windows related comments were deleted as being not relevant. 
See https://github.com/hashicorp/nomad/pull/9643 for context.

Add a build target for Apple Silicon (m1) macs.

Note that Go must have been built with c4f497da6f for
Nomad to work on darwin/arm64 (i.e. wait for go1.16).

Closes #9408

Parameterize it so we can arbitrary target other versions, if we
are doing some manual checking, specially in the beginning when we may
want to validate compatibilities for skip release upgrades.

Also, introduce `checkbuf` target so we can run buf linter without the
rest.

use beta