Prepare release 1.15.0

[0xnm]

What does this PR do?

This PR prepares release 1.15.0 of the Datadog Android Gradle Plugin.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release/1.15.0@c5ea7ed). Learn more about missing BASE report.

Additional details and impacted files

@@                Coverage Diff                @@
##             release/1.15.0     #304   +/-   ##
=================================================
  Coverage                  ?   77.96%           
  Complexity                ?      259           
=================================================
  Files                     ?       31           
  Lines                     ?      939           
  Branches                  ?      113           
=================================================
  Hits                      ?      732           
  Misses                    ?      152           
  Partials                  ?       55