When execing into a task, it's useful to be able to set some special
environment variables, namely `TERM` and language environment variable.

In this PR, we expose `env` parameter that takes an array of `KEY=VALUE`
values that gets thread all the way through to executors exec handling.

The main purpose is to allow configuring `TERM` for purposes of web ui,
as the appropriate value would depend on the terminal library and not
necessarily user friendly.

CLI
----------

This PR doesn't expose this configuration to CLI due to some
complexities:

* It's not as valuable to set environment variables there
(i.e. users can export their environment variables before running
commands)
* The `-e` flag is already used for escape character, and I'm unsure if
how to best proceed; I can see the appeal of repurposing `-e` to
env-variables as it's the most common thing
* We use the standard library `flags` package that doesn't support
string array flag to allow for multiple environment variables nicely.

As such, I've punted on supporting the CLI for another time as the need
arises.

External drivers and compatibility
----------

This PR makes some changes to the exec endpoint in drivers.  These
changes are binary backward compatible: existing drivers continue to run
against latest nomad binary as the grpc handler ignores the new `env`
field.  The drivers continue to compile as normal against the version
they vendored or depended on.

Though, when plugin authors upgrade the dependency they will need to
update code to either handle the `env` field or explicitly ignore it.

closes #6672

This is the basic code to add the Windows Service Manager hooks to Nomad.

Includes vendoring golang.org/x/sys/windows/svc and added Docs:
* guide for installing as a windows service.
* configuration for logging to file from PR #6429

there was a bad (localhost) URL in the vault docs (cherry pick of #6674)

Fixes #6645

update changelog

linter fixes

The LXC task driver documentation is missing for many of the optional
task config fields, and for the recently added `gc` field on the
driver configuration.

return a 404 if not found instead of redirect to ui

* Added firecracker-task-driver to community docs
Signed-off-by: Carlos Neira <cneirabustos@gmail.com>

website - add -moz-osx-font-smoothing for smooth firefox osx fonts

decompress response body from websocket error

return after request has been forwarded

If a websocket connection errors we currently return the error with a
copy of the response body. The response body from the websocket can
often times be completely illegible so remove it from the error string.

make alloc id empty for more reliable failure

un-gzip if content encoding header present

TestEvalBroker_Dequeue_Blocked() improve test readability

nomad: fix bug that didn't allow for multiple connect services in same tg

Consider devices in tasksUpdated

TestEvalBroker_PauseResumeNackTimeout() improve test readability

Co-Authored-By: Michael Schurter <mschurter@hashicorp.com>

to be updated to consider devices

updates default consul version to 1.6.1

nomad: TestEvalBroker_EnqueueAll_Dequeue_Fair() improve test readability