Prepare for 8.0.0~pre2 Release

[azeey]

🎈 Release

Preparation for 8.0.0~pre2 release.

Comparison to 7.6.0: gz-sim7_7.6.0...gz-sim8

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.

[azeey]

There are test failures related to #2008. I'm working on a fix.

[azeey]

@osrf-jenkins run tests please

[codecov]

Codecov Report

Merging #2178 (ef5813e) into gz-sim8 (c5cd260) will increase coverage by 0.53%.
The diff coverage is n/a.

❗ Current head ef5813e differs from pull request most recent head bb1365a. Consider uploading reports for the commit bb1365a to get more accurate results

@@             Coverage Diff             @@
##           gz-sim8    #2178      +/-   ##
===========================================
+ Coverage    65.49%   66.02%   +0.53%     
===========================================
  Files          323      323              
  Lines        30719    30719              
===========================================
+ Hits         20118    20281     +163     
+ Misses       10601    10438     -163     

see 5 files with indirect coverage changes