[ign-math6] Workflow updates

[chapulina]

• Add labeler workflow
• Add triage workflow
• Add Ubuntu CI workflow with Codecov upload
• Update badges
• Add CODEOWNERS
• This needs Script hooks gazebo-tooling/action-gz-ci#4 for the examples compilation to work.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (ign-math6@c272642). Click here to learn what that means.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             ign-math6     #117   +/-   ##
============================================
  Coverage             ?   99.50%           
============================================
  Files                ?       59           
  Lines                ?     5658           
  Branches             ?        0           
============================================
  Hits                 ?     5630           
  Misses               ?       28           
  Partials             ?        0           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c272642...bfccbab. Read the comment docs.

[maryaB-osr]

👍