[ign-rendering2] Workflow updates

[chapulina]

• Add labeler workflow
• Add triage workflow
• Add Ubuntu CI workflow with Codecov upload
• Update codecov badge
• Port CODEOWNERS

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (ign-rendering2@1774bea). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff                @@
##             ign-rendering2     #79   +/-   ##
================================================
  Coverage                  ?   7.93%           
================================================
  Files                     ?      24           
  Lines                     ?    1664           
  Branches                  ?       0           
================================================
  Hits                      ?     132           
  Misses                    ?    1532           
  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 1774bea...964a078. Read the comment docs.