Add support to HTTP(s) endpoint as Bucket source

[laozc]

The idea is to provide the ability to create a Bucket with a generic HTTP(s) endpoint for downstream consumption,
such as Kustomization controller which requires either Git/Bucket sources.

This could allow flux components to integrate with other in-cluster services providing HTTP access to resource manifest.

[hiddeco]

I am not sure I agree on expanding the Bucket source to allow this, as the proposed is a simple file downloader and not something which iterates over an HTTP endpoint.

Given this, I think people quickly would want to be able to compose a list of URLs to download and create an artifact out of, which isn't something the Bucket kind could be expanded to, as it would not fit with actual Bucket implementations.

[stefanprodan]

@laozc what you are proposing here is a major change to Flux that needs go over an RFC process. IMO fetching files from random HTTP/S servers is not in scope for the Bucket kind.

[laozc]

@stefanprodan Sure. Let me work on a RFC to discuss this further.

[stefanprodan]

@laozc I would close the PR opened for this, as we can't get that in, not in the current shape anyway.