[Java] Add an option to not generate equals/hashcode/toString

Description

The pojo.mustache template used for Java models always includes equals, hashcode and toString methods. There may be occurrences when they are not relevant, or we don't want them generated (the toString might reveal confidential information if the model is logged, the equals on all fields might not be relevant…).

Swagger-codegen version

3.0.47, not a regression as far as I can tell.

Command line used for generation

(using maven plugin)

Steps to reproduce

Generate for language java, spring, or logically any java-derived language.

Related issues/PRs

I couldn't find any.

Suggest a fix/enhancement

The simplest way to circumvent this would be to add an option not to generate those methods, or two separate options, maybe:

• generateToString (default: true)
• generateEqualsAndHashCode (default: true)

I suppose it could be handled in AbstractJavaCodegen.java + pojo.mustache.

Start with AbstractJavaCodegen.java and the pojo.mustache template, then run Java or Spring generation through the Maven plugin to observe the current output. Add configurable behavior for generating toString and equals/hashCode, preserving the default behavior, and verify that disabling the options removes the corresponding methods from generated models.