Switch to unclog for changelog management

[kasey]

What type of PR is this?

Other

What does this PR do? Why is it needed?

This PR replaces the current changelog PR check with a new workflow using our changelog management tool(unclog)[https://github.com/OffchainLabs/unclog] tool. Please see the unclog documentation for full details on how to satisfy the requirements of this workflow. In addition to the workflow changes, this PR contains:

• A changelog fragment porting the current Unreleased section of the changelog to a single fragment file.
• Edits to the current changelog to remove the Unreleased section.
• Edits to the the CONTRIBUTING.md document linking to the unclog documentation.

Which issues(s) does this PR fix?

The main pain point in our changelog management workflow is conflicts in CHANGELOG.md across PR branches causing headaches when merging PRs to develop. See the unclog documentation for more details.

Acknowledgements

• I have read CONTRIBUTING.md.
• I have made an appropriate entry to CHANGELOG.md.
• I have added a description to this PR with sufficient context for reviewers to understand this PR.

[nisdas]

Should we remove the current changelog.md file ?

[kasey]

Should we remove the current changelog.md file ?

This PR removes all changes to it since the last release. The plan going forward is to commit the updated changelog each time we run the release command, meaning the top section of CHANGELOG.md will always reflect the latest release, and unreleased changes will be in the changelog directory - there won't be an "unreleased" section any longer. If it turns out to be confusing to maintain the historical changelog in version control like this we can just remove it. But I think it seems valuable to preserve it here as a "backup" vs trusting github release mechanism to preserve the history.

[prestonvanloon]

One comment, otherwise LGTM

[prestonvanloon]

Discussed offline that the maximum artifact retention period is 90 days so we will need to address this in a follow up.

https://docs.github.com/en/actions/administering-github-actions/usage-limits-billing-and-administration#artifact-and-log-retention-policy