changelog: add go-changelog templates and tooling

[mikemorris]

Changes proposed in this PR:

• Adds template files used by go-changelog and make tasks to generate a changelog section for a specific release from changelog entry files associated with pull requests.
• Adds a CI workflow to check for changelog entries in PRs.

TODO:

• Add make tasks
  • make changelog for changelog-build
  • make changelog-entry for creating a new blank changelog entry file, prompt for entry type
    • Add upstream tool for generating changelog entries
      • cmd: add changelog-entry generation tool go-changelog#19
      • changelog-gen to generate changelog entries for local setup go-changelog#13
        • minor cleanup of changelog-gen command, rename to changelog-entry dhiaayachi/go-changelog#1
  • make changelog-check for validating entries, as described in Add CHANGELOG file contents linting terraform-provider-aws#17135 - would be nice to possibly have this as a git hook if the commit contains a changelog entry
    • Extract changelog-check tool upstream out of changelog-pr-body-check, which is a specific implementation oriented around having contributors add changelog notes in the body of a GitHub PR description rather than as a separate file, and has assumptions in the error handling based on the Google Cloud Platform Terraform provider "magic modules" workflow
      • add changelog-check command go-changelog#22
• Remove note from PR template about only HashiCorp engineers adding changelog entries.
• Add CI check to ensure changelog entries on all PRs and ensure that entries follow valid formatting
  • Copy GitHub CI workflow from Consul https://github.com/hashicorp/consul/blob/main/.github/workflows/changelog-checker.yml
  • Add make changelog-check to workflow
• Add workflow/no-changelog label to skip CI check
• Check for spelling errors like .github/workflows/changelog: add .changelog dir to PR path and to misspell run command terraform-provider-aws#17464?
  • aspell might be a better option than the misspell Go library that hasn't been maintained in four years, but too much of a lift and possible false negatives to implement right now
• Add changelog generation notes to release docs

How I've tested this PR:

make changelog

Running

LAST_RELEASE_GIT_TAG=v0.1.0 make changelog

should generate

IMPROVEMENTS:

* changelog: add go-changelog templates and tooling [[GH-101](https://github.com/hashicorp/consul-api-gateway/issues/101)]

make changelog-check

cat ./changelog/101.txt | make changelog-check

should validate the changelog entry for .changelog/101.txt successfully with exit code 0

echo "foo" | make changelog-check

should check that the string foo is not a valid changelog entry, with exit code 1

echo "\`\`\`release-note:bar\`\`\`" | make changelog-check

should check that the string bar is not a valid changelog entry type and list the valid configured changelog entry types, with exit code 1

make changelog-entry

make changelog-entry

should detect that the current branch has an open pull request and start an interactive workflow to write a valid changelog entry at ./changelog/101.txt

How I expect reviewers to test this PR:

• Test the changelog generation and validation commands through make tasks
• The current template at .changelog/changelog.tmpl is a slight modification of the stock template from go-changelog and is mostly similar to https://github.com/hashicorp/consul/blob/main/.changelog/changelog.tmpl - we should review together and determine what format or tweaks we'd like
• add basic support for configurable changelog entry types go-changelog#21 introduces support for configuring a list of valid changelog entry types - a suggest list has been added at .changelog/types.txt, we should discuss whether this list is sufficient for our needs
• Do we want to implement the changelog-entry-in-PR-body style used by https://github.com/hashicorp/go-changelog/tree/main/cmd/changelog-pr-body-check (and similar to upstream Gateway API?) or keep the file/label-based workflow?

Checklist:

• Tests added (CI validation)
• CHANGELOG entry added

  HashiCorp engineers only, community PRs should not add a changelog entry.
  Entries should use present tense (e.g. Add support for...)

Refs prior implementations in:

• https://github.com/GoogleCloudPlatform/magic-modules/blob/main/.ci/RELEASE_NOTES_GUIDE.md to power https://github.com/hashicorp/terraform-provider-google/
• Introducing go-changelog consul#8387
• Adopt go-changelog in Nomad nomad#10825
• Changelog Automation terraform-provider-aws#16215

[hashicorp-cla]

All committers have signed the CLA.

[mikemorris]

The current workflow for changelog generation only happens at release time - for future work we may want to consider implementing hashicorp/go-changelog#5 to allow the CHANGELOG.md file to be updated automatically as PRs are merged so users can see changes which have been merged and will be included in the next release.

[nathancoleman]

Nice work! Excited to see this