chore(docs): clarify gunicorn/gevent documentation

[Yun-Kim]

We've had a bit of confusion with our recent changes to our gunicorn documentation (#5228, #5248). This PR clarifies the gunicorn documentation and changelog to make it clear for users that ddtrace-run supports Gunicorn when not being run with Gunicorn's gevent worker type.

This should fix #5248.

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed.
• Documentation is included (in-code, generated user docs, public corp docs).
• Author is aware of the performance implications of this PR as reported in the benchmarks PR comment.

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer is aware of, and discussed the performance implications of this PR as reported in the benchmarks PR comment.

[pr-commenter]

Benchmarks

Comparing candidate commit c5da033 in PR branch yunkim/clarify-gunicorn with baseline commit 58017b1 in branch 1.x.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 56 cases.

[Yun-Kim]

Closing as #5105 has made this obsolete.