DOC: Last changes to release notes for 1.5.0 release
- [X] closes #48248

Updating date, clean up, and adding contributors to the 1.5.0 release. @pandas-dev/pandas-core I think this should be the last blocker for the 1.5.0 release. If merging anything else after this PR and before the release, please let me know.
https://github.com/pandas-dev/pandas/pull/48619

This one would be ready, but no big deal if we do for 1.5.1 I believe #48620 is all set to go. It's a somewhat substantial fix to a widespread performance regression, but I think it would be okay to wait for 1.5.1. Not a blocker in my opinion. Thx @datapythonista 