Enable storage server to serve https

[kvmw]

Enables https on storage server by setting storage-https-enabled flag and passing storage-cert-path.

• storage-https-enabled is a bool, defaults to false
• storage-cert-path is a directory containing tls.crt (certificate) and tls.key (private key). It can be a Secret volume in k8s env.

[pjbgf]

@kvmw Thank you very much for your PR.

This topic came up in the Flux dev meeting a few weeks ago, so I created a RFC to formalise what we believe an implementation should look like. Some details are still up for debate, so I would ask you to engage on that PR in case you agree/disagree with the approach.

Once the RFC is in an implementable state, this PR could be the source controller implementation.