Remove appassembler-maven-plugin

[lintool]

Deprecation in JDK 21 of plugin requires an entirely new approach to launch classes.

[WARNING] 
[WARNING] Plugin validation issues were detected in 3 plugin(s)
[WARNING] 
[WARNING]  * org.apache.maven.plugins:maven-javadoc-plugin:3.6.3
[WARNING]  * com.github.eirslett:frontend-maven-plugin:1.12.1
[WARNING]  * org.codehaus.mojo:appassembler-maven-plugin:2.1.0
[WARNING] 
[WARNING] For more or less details, use 'maven.plugin.validation' property with one of the values (case insensitive): [BRIEF, DEFAULT, VERBOSE]
[WARNING] 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.68%. Comparing base (c0f4347) to head (e6a94f7).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2444   +/-   ##
=========================================
  Coverage     66.68%   66.68%           
  Complexity     1417     1417           
=========================================
  Files           213      213           
  Lines         12169    12169           
  Branches       1488     1488           
=========================================
  Hits           8115     8115           
  Misses         3539     3539           
  Partials        515      515           

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[lintool]

This is ready to be reviewed. Yes, it's a massive change since we've removed all the target/appassembler/bin launch scripts...