Move `github.com/fluxcd/source-controller/pkg` to either `source-controller/internal/bucket` or `fluxcd/pkg/bucket`

[matheuscscp]

The source-controller is the only Flux controller exposing a public /pkg besides /api. This package has code for accessing Bucket providers. To make it aligned with everything else, we should decide on either moving it to fluxcd/pkg/bucket and continue supporting it as a GA API (starting from v1.0.0), or moving it to source-controller/internal/bucket.

[matheuscscp]

There are no public imports of these packages:

• https://pkg.go.dev/github.com/fluxcd/source-controller/pkg/azure?tab=importedby
• https://pkg.go.dev/github.com/fluxcd/source-controller/pkg/gcp?tab=importedby
• https://pkg.go.dev/github.com/fluxcd/source-controller/pkg/minio?tab=importedby

[stefanprodan]

I’m in favor of internal/bucket

[matheuscscp]

+1 internal/bucket

[cappyzawa]

+1 internal/bucket

[cappyzawa]

Since I am currently working on the bucket-related changes in #1862, I plan to tackle this after that PR is merged. Given the current status, I intend to move the code to internal/bucket.

[stefanprodan]

I'll take this as I want to refactor the project structure a little bit more than just moving the bucket code.