Prepare for 7.3.0

[bperseghetti]

🎈 Release

Preparation for 7.3.0 release.

Checklist

• [x] Asked team if this is a good time for a release
• [x] There are no changes to be ported from the previous major version
• [ ] No PRs targeted at this major version are close to getting in
• [x] Bumped minor for new features, patch for bug fixes
• [x] Updated changelog
• [ ] Updated migration guide (as needed)
• [ ] Link to PR updating dependency versions in appropriate repository in gazebo-release (as needed):

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 79.39%. Comparing base (92e02c3) to head (b7b2e06). Report is 23 commits behind head on gz-physics7.

:exclamation: Current head b7b2e06 differs from pull request most recent head e72959d

Please upload reports for the commit e72959d to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## gz-physics7 #659 +/- ## =============================================== + Coverage 78.32% 79.39% +1.06% =============================================== Files 140 144 +4 Lines 8069 8473 +404 =============================================== + Hits 6320 6727 +407 + Misses 1749 1746 -3 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[bperseghetti]

@azeey did the windows CI machine die?

[scpeters]

@azeey did the windows CI machine die?

I just restarted the job. We've been having trouble with the windows machines disconnecting

[azeey]

Windows is having a hard time today. It passed in https://build.osrfoundation.org/job/gz_physics-pr-win/276/ so I'll go ahead and merge this.

[peci1]

There's a possible "fixup" for this release (or rather a piggyback request) in https://github.com/gazebosim/gz-physics/pull/641#issuecomment-2190018675 .