Add message definitions for the parameter component

[ivanpauno]

🎉 New feature

Summary

Add message definitions to be used by the ignition transport parameter component.
See gazebosim/gz-transport#305.

Test it

See gazebosim/gz-sim#1431 for details of a demo.
Replaces #211.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• 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.

[codecov]

Codecov Report

Merging #241 (c1510f7) into ign-msgs8 (8e10c8d) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           ign-msgs8     #241   +/-   ##
==========================================
  Coverage      85.38%   85.38%           
==========================================
  Files              9        9           
  Lines            951      951           
==========================================
  Hits             812      812           
  Misses           139      139           

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[mjcarroll]

I think that Any makes more sense if everything is going to stay protobuf.

[codecov]

Codecov Report

Merging #241 (69fde66) into ign-msgs8 (065a3ce) will not change coverage.
The diff coverage is n/a.

❗ Current head 69fde66 differs from pull request most recent head abc8ed6. Consider uploading reports for the commit abc8ed6 to get more accurate results

@@            Coverage Diff             @@
##           ign-msgs8     #241   +/-   ##
==========================================
  Coverage      96.64%   96.64%           
==========================================
  Files              9        9           
  Lines            953      953           
==========================================
  Hits             921      921           
  Misses            32       32           

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[caguero]

Looks good to me. Just a minor comment but I'm approving.

[ivanpauno]

@caguero friendly ping