pystac v1.15.0 release checklist

Since we refactored all the extensions to their own packages in https://github.com/stac-utils/pystac/pull/1650, we will move a little more slowly for the v1.15.0 release of PySTAC. The plan is: - [ ] Update our release workflow to release each extension's package, in addition to the core packages - [ ] Update the main packages and each extensions' version to have a `-rc.0` suffix (we've tried to do this with **release-please** but have failed, so falling back to doing it manually) - [ ] Locally, manually create `-rc.0` tags for the main packages and each extensions - [ ] Push each tag, which should fire off publishing - [ ] Check for errors/problems and correct - [ ] Once everthing's ok, release the non-rc versions