[Repository] refactor the auth support to share code and remove duplication

[dlaloue-vmware]

The repository service API is implemented by the three plugins helm, flux and carvel. There are several aspects of the implementation which is not plugin specific and hence is duplicated.

This issue is about refactoring the code to make common code that is not plugin specific - e.g. detecting the type of the secret, setting the owner reference, CRUD the secret etc...