[REQ] [java] create a builder pattern for the models

[jpfinne]

Is your feature request related to a problem? Please describe.

A good builder pattern generation can solve many issues:

• initialize readonly values in the java generator
• make it similar to the lombok builder that people are used to.
• introduce immutability

Lombok can be used the generate builders. But the introduction of lombok creates more issues (#17793)

Describe the solution you'd like

Add a builder inner class
Add a static builder() method
Add a toBuilder() method

Describe alternatives you've considered

Reuse the builder from javaJAXRSServerCodeGen.
Fix the lombok generation issues.