Enable codecov

[ajschmidt8]

Description

This PR enables codecov for GitHub Actions for rmm. The codecov results can be placed in the directory defined by the RAPIDS_COVERAGE_DIR variable, which is set in our shared workflows.

Additionally, this PR configures the unit test results to be placed in the directory defined by the RAPIDS_TESTS_DIR variable, which is also set in our shared workflows.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (branch-23.02@d132e52). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@              Coverage Diff               @@
##             branch-23.02   #1171   +/-   ##
==============================================
  Coverage                ?   0.00%           
==============================================
  Files                   ?       5           
  Lines                   ?     406           
  Branches                ?       0           
==============================================
  Hits                    ?       0           
  Misses                  ?     406           
  Partials                ?       0           

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[bdice]

Looks good, after you merge the upstream PR and change the branch names back.