Release docs

[MarkWolters]

This PR adds a skeleton for adding robust release notes for all features included in a specific release, as well as a github action for combining individual contributor release notes into a single release-wide markdown file to be included as a release artifact.

[github-actions]

Before you submit for review:

• Does your PR follow guidelines from CONTRIBUTIONS.md?
• Did you summarize what this PR does clearly and concisely?
• Did you include performance data for changes which may be performance impacting?
• Did you include useful docs for any user-facing changes or features?
• Did you include useful javadocs for developer oriented changes, explaining new concepts or key changes?
• Did you trigger and review regression testing results against the base branch via Run Bench Main?
• Did you adhere to the code formatting guidelines (TBD)
• Did you group your changes for easy review, providing meaningful descriptions for each commit?
• Did you ensure that all files contain the correct copyright header?
• Did you add documentation for this feature to the release notes directory?

If you did not complete any of these, then please explain below.

[r-devulap]

This look great. One suggestion: we could make the release note generation more structured by standardizing the source filenames to <#PR>..md (eg 668.performance.md, 659.newfeature.md). The workflow can then automatically group entries by tag (e.g., Performance, New Features, Bug Fixes) in the release notes (making it more structured) instead of relying on manual order. It also makes it easy to add a link to the corresponding PR in the notes itself for easy reference.

[MarkWolters]

Great idea @r-devulap, pushed changes to that effect now

[r-devulap]

Awesome, do we want to regenerate the 4.0.0.RC8 release notes based on the PR/Tag format?

[r-devulap]

Add bench for benchmarks related?