feature(config): Add go-sockaddr templating support to nomad consul address

[Nkmol]

This PR adds support for go-sockaddr/template in the consul address Stanza.

As noted in the issue, this becomes especially useful when you want to pair your nomad agent to the consul private network agent in a dynamic fashion.

Fixes: #11062

Special note to the reviewer

A check has been added to only support one single IP in the Stanza, as was done in other places using ParseSingleIPTemplate. However, I think in the years Hashicorp defines this in their shared package: https://github.com/hashicorp/go-secure-stdlib/blob/7166b1cdf6a6eb1311247e34feae17eaf7b657bf/listenerutil/parse.go#L374
Adding an extra dependency to the repo of go-secure-stdlib might not be something preferable. If this is still preferable, I could add this extra import.

---

This is my first contribution to this project and the first time touching Go, so any tips or directions for improvement is always welcome :)

[hashicorp-cla]

All committers have signed the CLA.

[DerekStrickland]

Hi @Nkmol . Thanks for contributing!

I'm going to take a look today and talk to the team about your contribution.

[DerekStrickland]

I found one thing right away that is a blocker. See comment about panic.

[tgross]

Hi @Nkmol! Thanks for this PR, this is looking really good. I've left a few comments but once those are resolved I imagine we can get this shipped as part of Nomad 1.3.0

If you'd like, you can add a changelog file too. That'd be a text file at .changelog/12084.txt formatted similar to .changelog/12079.txt.

[Nkmol]

Thanks @shoenig and @tgross for the thorough review. Based on the feedback, I changed the following:

• Imported the https://github.com/hashicorp/go-secure-stdlib/releases/tag/listenerutil%2Fv0.1.4 module
  Importing this module, however, introduced more dependencies than I was expecting. My gut feeling is telling me the dependencies added and changed might be too much out of scope of this PR. I am having a hard time assessing the mod.go changes :) Let me know what you think about this.
• Implemented table-driven tests
  TIL :) I did not know about this and tried to make them as parallel runnable as possible being aware of the Go Routine bug.
• Migrated from Go asserts to testify

[tgross]

LGTM! I'll get this merged once CI is done and it'll ship in Nomad 1.3.0. Thanks again @Nkmol!

Resolved

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