7.0.0 release

[nkoenig]

Signed-off-by: Nate Koenig [email protected]

🎈 Release

Preparation for 7.0.0 release.

Changelog complete in #506

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 #509 (87da3e7) into gz-math7 (05b9dc6) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           gz-math7     #509   +/-   ##
=========================================
  Coverage     99.70%   99.70%           
=========================================
  Files            77       77           
  Lines          7007     7007           
=========================================
  Hits           6986     6986           
  Misses           21       21           

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