Support multiple SDKs and rebrand to rewrite-feature-flags

[timtebeek]

What's changed?

Rename module to rewrite-feature-flags.
Change packages to match new structure.
Add support for

• FF4j
• OpenFeature
• Unleash

What's your motivation?

Become a more general wrapper for other SDKs, similar to what we've seen with

• https://github.com/openrewrite/rewrite-logging-frameworks

• https://github.com/openrewrite/rewrite-testing-frameworks

• Fixes Rebrand recipe module to rewrite-feature-flags #26

• Fixes Support the OpenFeature Provider #6

Anything in particular you'd like reviewers to focus on?

Any concerns with the package change for existing recipes?
If needed we once-upon-a-time had a recipe to fix renames.

Anyone you would like to review specifically?

@shanman190

Have you considered any alternatives or workarounds?

Separate git repository per vendor seemed too heavy handed to maintain.
Separate submodules per vendor seemed too early, even if that leads to better classpath separation.
Briefly explored Togglz, but since that uses Enums it would need a dedicated recipe implementation.

• https://www.togglz.org/documentation/configuration

Any additional context

• https://ff4j.org/#10min
• https://openfeature.dev/docs/reference/technologies/server/java/
• https://docs.getunleash.io/feature-flag-tutorials/java

[shanman190]

This also will close #6 as the implementation was included here.