Increase user flexibility regarding generation of filenames

[M-Davies]

With the merge of adoptium/temurin-build#2132 , user's have a lot more flexibility on what and where and how they can build Java binaries. However, the limiting factor at the moment are hardcoded filenames inside directories within the scripts. These will force user's who are looking to benefit from adoptium/temurin-build#2132 to use our filenames without being able to pick their own. This should not be the case and the scripts should be smart enough to tell if they are looking at a directory, adopt file or user file. Examples below:

• https://github.com/AdoptOpenJDK/openjdk-build/blob/c051c3fe1d4b3744963ba20572f848967dfbd21e/pipelines/build/openjdk8_pipeline.groovy#L87
• https://github.com/AdoptOpenJDK/openjdk-build/blob/b8c70fc62f9e710b90cbe0aff6801cbaea86fcd5/pipelines/build/regeneration/jdk8_regeneration_pipeline.groovy#L121
• https://github.com/AdoptOpenJDK/openjdk-build/blob/b8c70fc62f9e710b90cbe0aff6801cbaea86fcd5/pipelines/build/regeneration/build_pipeline_generator.groovy#L166
• https://github.com/AdoptOpenJDK/openjdk-build/blob/b8c70fc62f9e710b90cbe0aff6801cbaea86fcd5/pipelines/build/prTester/pr_test_pipeline.groovy#L88

[M-Davies]

Related #60