Add error prone checks for internal javadoc and private constructors

[jack-berg]

Ports build automation from opentelemetry-java-instrumentation/custom-checks to add additional custom error prone checks

• Ensure that utility classes have private constructors
• Ensure public internal classes have standard boilerplate

Resolves #6798.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.49%. Comparing base (2e8bf7f) to head (c8f04ed).
Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6844      +/-   ##
============================================
- Coverage     90.49%   90.49%   -0.01%     
  Complexity     6598     6598              
============================================
  Files           731      731              
  Lines         19735    19735              
  Branches       1938     1938              
============================================
- Hits          17860    17859       -1     
  Misses         1283     1283              
- Partials        592      593       +1     

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[laurit]

did you deliberately keep the javaagent package?

[jack-berg]

Nope, good catch!