Prepare for 8.0.0~pre3 Release

[azeey]

🎈 Release

Preparation for 8.0.0~pre3 release.

Comparison to 7.4.2: gz-rendering7_7.4.2...gz-rendering8

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]

Codecov Report

Merging #924 (c43a921) into gz-rendering8 (598cd41) will not change coverage.
Report is 1 commits behind head on gz-rendering8.
The diff coverage is n/a.

❗ Current head c43a921 differs from pull request most recent head 7d95293. Consider uploading reports for the commit 7d95293 to get more accurate results

@@              Coverage Diff               @@
##           gz-rendering8     #924   +/-   ##
==============================================
  Coverage          75.15%   75.15%           
==============================================
  Files                177      177           
  Lines              16830    16830           
==============================================
  Hits               12649    12649           
  Misses              4181     4181