Add degree as an optional unit for rotation in GzPose

[AzulRadio]

Signed-off-by: youhy haoyuan2019@outlook.com

New feature

Summary

Add degree as an optional unit for rotation in GzPose. Radian is set to default.

Test it

Can be tested with gazebosim/gz-sim#1642

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.

[codecov]

Codecov Report

Merging #475 (c3754d0) into ign-gui3 (c3df98d) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           ign-gui3     #475   +/-   ##
=========================================
  Coverage     69.81%   69.81%           
=========================================
  Files            29       29           
  Lines          3273     3273           
=========================================
  Hits           2285     2285           
  Misses          988      988           

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[jennuine]

LGTM, just one minor comment