Change Nephio builds to remove generated code form the repositories

[liamfallon]

In both the "nephio" and "porch" repositories, generated code is checked into the repositories.

As a rule, generated files should not ever be checked into a repository and is bad practice. They should be generated as part of the build as a precompile step in the build and placed in a temporary location were the compile step of the build can access them. This:

• reduces the risk of misalignment happening here the metadata used to generate the generated files gets out of sync with the compiled code
• reduces the risk of tooling used to generate code changing and causing different versions of generated code to be rendered for the same metadata
• reduces the volume of code that needs to be maintained
• avoids the risk of developers accidentally (or worse pragmatically) modifying the generated code
• reduces the size of PRs

[efiacor]

I'm not 100% sure but I think the operator sdk is a special case.
As part of the project generation it creates:

• The api/v1alpha definitons
• The related CRDs
• Lots of stuff under the config dir

Some of the above is used internally as part of the testing setup and run. To build these each time would not be ideal in my opinion.