directly support java-gradle-plugin projects

[gabrielittner]

Addresses issues mentioned in #82. Like Kotlin mpp the java-gradle-plugin creates it's own publications. We need to configure those instead of creating our own.

Also closes #111

[gabrielittner]

@ZacSweers this should fix your issues

[codecov]

Codecov Report

Merging #115 into master will decrease coverage by 0.89%.
The diff coverage is 13.79%.

@@             Coverage Diff             @@
##             master     #115     +/-   ##
===========================================
- Coverage     35.29%   34.39%   -0.9%     
- Complexity       49       51      +2     
===========================================
  Files            21       21             
  Lines           425      439     +14     
  Branches         70       73      +3     
===========================================
+ Hits            150      151      +1     
- Misses          246      258     +12     
- Partials         29       30      +1

Impacted Files	Coverage Δ	Complexity Δ
...nniktech/maven/publish/UploadArchivesConfigurer.kt	82.85% <0%> (-2.44%)	10 <0> (ø)
...vanniktech/maven/publish/MavenPublishConfigurer.kt	0% <0%> (ø)	0 <0> (ø)	⬇️
...vanniktech/maven/publish/BaseMavenPublishPlugin.kt	60.86% <50%> (-1.93%)	7 <2> (+2)

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