Enable proper maintainable code generation

[maxandersen]

Describe the bug
This is not news, but couldn't find an issue representing it so writing this down here and we can link it up if need be.

In 1.3.1 we are trying to switch code generation to generate for java 11 instead of java 8 based on what version of java the user is running.

That revealed a few things;

1. it breaks former 1.3.x plugins as now the templates introduces a new variable that 1.3.0 wont set.

2. to fix Switch to the Maven distributed copy of the SubstrateVM annotations #1 it was suggested to use freemarker default value fallbacks so if the variable is not set a reasonable default is generated - problem is at some point the code generation stopped using freemarker (but still called the files .ftl) and now its all done by string replacement making it impossible to have the codegeneration templates have fallbacks to stay compatible.

3. assumed reason for stopping to use freemarker was to let code.quarkus run in native mode; that was probably not a good idea to do before we actually had something like that qute that can run in native mode. otherwise we are stuck with either not progressing the templates in minor releases or breaking users using project create since the default behavior is to pick the latest released platform.

outcome of this is two-fold I would say:

• consider removing the behavior where we pick up the latest released platform (at least until this issue is fixed)
• consider having a separate file (available online, maybe via maven) to outline what version of platform we should pickup instead of making it "always the latest-greatest" (done in past effectively for jbosstools config.properties code is here.
• consider using qute to make generation feasible in native for code.quarks (I dont think it can be in long run if we need it to target multiple versions) but at least have some proper template language that can handle fallback defaults.

[ia3andy]

This is done