Fixes #6041

Unlike all other Consul operations, boostrapping requires Consul be
available. This PR tries Consul 3 times with a backoff to account for
the group services being asynchronously registered with Consul.

Register connect enabled group services with Consul

Adds a check for differences in `job.Diff` so that task group networks
and services, including new Consul connect stanzas, show up in the job
plan outputs.

Fixes #6042

Add new task group service hook for registering group services like
Connect-enabled services.

Does not yet support checks.

Bump up github.com/hashicorp/go-syslog for better BSD support

add node.region to interpolation documentation

UI: Allocation file system explorer

UI: Use the standard empty message when an fs dir is empty

vendor: update testify to v1.4.0

This lets us turn Mirage logging on without editing any
files, which makes it easier to switch between branches.

Block rpc handling until state store is caught up

* structs: use seperate SidecarTask struct for sidecar_task stanza and add merge

* nomad: merge SidecarTask into proxy task during connect Mutate hook

link-local addresses can be fingerprinted

Adds an example job for Consul Connect integration as well as an
annotated example job.

UI: Alloc FS: File Viewer

Add a link to the discussion forum on the resources page

Added note to document that link-local addresses can be fingerprinted in
cases where no routable address can be found.  Crosslinked to
`"fingerprint.network.disallow_link_local"` because they are somewhat
related and it is documented at a reasonable distance from this setting.

docker: Fix issue where an exec may never timeout

--payload -> --data for curl; consistent @payload

syntax fix; add example for alloc exec -task

NetworkIsolation was left out of the task config when using an
external task driver plugin

* nomad: add admission controller framework

* nomad: add admission controller framework and Consul Connect hooks

* run admission controllers before checking permissions

* client: add default node meta for connect configurables

* nomad: remove validateJob func since it has been moved to admission controller

* nomad: use new TaskKind type

* client: use consts for connect sidecar image and log level

* Apply suggestions from code review
Co-Authored-By: Michael Schurter <mschurter@hashicorp.com>

* nomad: add job register test with connect sidecar

* Update nomad/job_endpoint_hooks.go
Co-Authored-By: Michael Schurter <mschurter@hashicorp.com>

Consul Connect must route traffic between network namespaces through a
public interface (i.e. not localhost). In order to support testing in
dev mode, users needed to manually set the interface which doesn't
make for a smooth experience.

This commit adds a facility for adding optional parameters to the
`nomad agent -dev` flag and uses it to add a `-dev=connect` flag that
binds to a public interface on the host.