Move the Maven plugins to a separate repository and release cycle

[reckart]

Describe the refactoring action
Move the Maven plugins to a separate repository and release cycle.

Expected benefit
Currently, we build the UIMA Maven plugins as part of the UIMA Java SDK. However, it is not possible in Maven to use a plugin in the same reactor it is built in. The best option we have currently is to hard-code an older version of the plugins into the build.
It would probably be cleaner and clearer if the Maven plugins would reside in their own repository and had their own release cycle separate from the UIMA Java SDK.

Here is how it currently manifests itself if we try to use the plugin built from the current reactor. In fact, it does not use it but tries to obtain it from the SNAPSHOT repo:

[INFO] --- jcasgen:3.6.0-SNAPSHOT:generate (default) @ uimafit-core ---
Warning:  The POM for org.apache.uima:jcasgen-maven-plugin:jar:3.6.0-20241118.151434-44 is invalid, transitive dependencies (if any) will not be available: 6 problems were encountered while building the effective model for org.apache.uima:jcasgen-maven-plugin:3.6.0-SNAPSHOT
Error:  'dependencies.dependency.version' for org.sonatype.plexus:plexus-build-api:jar is missing. @ 
Error:  'dependencies.dependency.version' for junit:junit:jar is missing. @ 
Error:  'dependencies.dependency.version' for org.assertj:assertj-core:jar is missing. @ 
Error:  'dependencies.dependency.version' for org.apache.maven:maven-compat:jar is missing. @ 
Error:  'dependencies.dependency.version' for org.apache.maven.plugin-testing:maven-plugin-testing-harness:jar is missing. @ 
Error:  'dependencies.dependency.version' for org.slf4j:slf4j-jdk14:jar is missing. @ 

See also: https://stackoverflow.com/questions/17284553/maven-plugin-as-dependency-in-multi-module-project

I had a quick look at your project and found, that the "generator" plugin is part of the multimodule project and it is used (with the same version) within this project. This is not a legal use! You have to provide all required plugins from outside the reactor!

The reason for this is, that maven tries to fill the reactor and determine all required plugins beforehand. Then it starts the build. Maven cannot perform this, if the generator plugin is part of the project.

The extra release cycle should not be too bad because we rarely change things that actually affect the plugins or the plugins themselves.