Remove PowerMock, Move to JUnit 5, target Java 8 again.

[simonmarty]

Issue #, if available:

Description of changes:

• Move to JUnit 5.
• Move to Mockito 5.
• Remove PowerMock.
• Moved from system-rules to system-stubs-jupiter since the first is not supported on JUnit 5.
• Updated all dependencies
• Updated the GitHub action workflow to build using JDK 17. (JDK 11 minimum is required for system-rules-jupiter, the library output is still Java 8 compatible.
• Set the maven-compiler-plugin target version to Java 8 using release. Explanation here.
• Enable auto-publish on the Maven sonatype plugin.
• Move from mockito-inline to mockito-core and its JUnit 5 plugin. The default mockmaker is mockito-inline in Mockito 5.
• Silence some test warnings by enabling dynamic agent loading. Mockito and systemstubs use byte-buddy to intercept calls.

This also fixes code coverage output.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.24%. Comparing base (0f59cbb) to head (8682a80).

Additional details and impacted files

@@              Coverage Diff              @@
##                 v2     #289       +/-   ##
=============================================
+ Coverage     24.86%   82.24%   +57.37%     
- Complexity       41      143      +102     
=============================================
  Files            12       12               
  Lines           366      366               
  Branches         45       45               
=============================================
+ Hits             91      301      +210     
+ Misses          273       58      -215     
- Partials          2        7        +5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.