Make Kiota.Builder.Plugins.PluginsGenerationService generic over the output kind

[calebkiage]

How the class works now:

The Kiota.Builder.Plugins.PluginsGenerationService is used to generate a plugin manifest from an OpenAPI document. It receives a working directory path as a string and generates plugin files into that path.

Why I want to change it

The current strategy works well but I see it becoming harder to maintain and test as more features are added to the type. It also makes it hard to test logic of individual units. For example, writing a test independent of the file system is currently not possible. That means that unit tests are effectively integration tests and require a lot of boilerplate code to write. This increases the development time of features in the class. I think this makes the class brittle and increases the maintainers' technical debt.

How I want to change it

I would like to split the type into multiple modular types that serve specific purposes. I haven't come up with a broken down design yet, but I would imagine the first big win is separating out the file IO from the type. This will unlock the possibility of using tests that work on in-memory data. An integration test could then be created to test the file system access.

How I would implement it

TBD