Prepare for 8.0.0~pre2 Release

[azeey]

🎈 Release

Preparation for 8.0.0~pre2 release.

Comparison to 7.2.1: https://github.com/gazebosim/gz-gui/compare/gz-gui7_7.2.1...gz-gui8

Checklist

• [ ] Asked team if this is a good time for a release
• [ ] There are no changes to be ported from the previous major version
• [ ] No PRs targeted at this major version are close to getting in
• [ ] Bumped minor for new features, patch for bug fixes
• [ ] 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

Merging #578 (af03d09) into gz-gui8 (84170fb) will not change coverage. The diff coverage is n/a.

:exclamation: Current head af03d09 differs from pull request most recent head b53780b. Consider uploading reports for the commit b53780b to get more accurate results

@@           Coverage Diff            @@
##           gz-gui8     #578   +/-   ##
========================================
  Coverage    68.07%   68.07%           
========================================
  Files           38       38           
  Lines         5369     5369           
========================================
  Hits          3655     3655           
  Misses        1714     1714