Ionic changelog

[caguero]

🎉 New feature

Part of gazebo-tooling/release-tools#1092

Summary

Update changelog for gz-plugin 3.0.0, with an estimated release date just a little before the community meeting.

Test it

Compare to gz-plugin2_2.0.3...main

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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.