Prepare for 6.0.0 pre1 release

[iche033]

🎈 Release

Preparation for 6.0.0-pre1 release.

Comparison to ign-rendering5: ign-rendering5...prep_6.0.0-pre1

Needed by <PR(s)>

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 ignition-release (as needed): Depend on ign-cmake 2.3 gazebo-release/gz-rendering6-release#3

Note to maintainers: Remember to use Squash-Merge

[codecov]

Codecov Report

Merging #417 (0356464) into main (7aade51) will not change coverage.
The diff coverage is n/a.

❗ Current head 0356464 differs from pull request most recent head 7484f42. Consider uploading reports for the commit 7484f42 to get more accurate results

@@           Coverage Diff           @@
##             main     #417   +/-   ##
=======================================
  Coverage   55.06%   55.06%           
=======================================
  Files         191      191           
  Lines       19265    19265           
=======================================
  Hits        10608    10608           
  Misses       8657     8657           

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[chapulina]

🚢 it