Align references to Secrets within all Source APIs

[aryan9600]

Historically all Source APIs used a single monolithic Secret for all sorts of configuration. But this is no longer true since there are Sources that have multiple Secret refs, for e.g.OCIRepository with its .spec.secretRef for auth credentials and .spec.certSecretRef for TLS certificates. Thus, to align how all Sources deal with Secrets, we need to make sure that all Source APIs drop the usage of monolithic Secrets and incorporate multiple Secret refs to configure different things.

Atm, only HelmRepository needs to be aligned with the new standard. This shall be done by adding a new field .spec.certSecretRef which would specify the Secret containing the TLS authentication data and deprecating support for the certFile, keyFile, caFile keys in the Secret specified in .spec.secretRef. Support for these keys will be fully removed when HelmRepository graduates to v1.