Make cloud providers modular and optional

[morey-tech]

The quickstart currently requires Azure and AWS credentials and doesn't support GCP. This becomes a barrier for people to spin up the BACK stack if they don't have those accounts.

Desired outcome: each cloud provider should be opt-in so that users can get started with whatever cloud provider they prefer.

Implementation details are up for discussion on the issue.

[kurktchiev]

So, as it stands with the new Porter install, clouds ARE optional, and the documentation needs more clarity in this spot. What you end up with, though, is needing help to provision clusters. What this starts us down is:

• How do we go about "bring your own clusters."
  • @djeremiah pointed to some resources in crossplane that would allow us to "auto discover" clusters under a provider
  • @kurktchiev was also suggesting a way to "import" only a specific cluster: kind, minikube, k3d, gke, whatever
• Are there any limitations to BYOC? I don't see what there would be, but it's more of a Backstage thing to look at and see if we can make the plumbing work with the catalog on manual import of an endpoint.

[kurktchiev]

this ties into #16 so might mark one a dupe of the other

[agardnerIT]

This confused me too. I want to spin up (experiment) locally with kind and yet I'm still asked for AWS and Azure creds.