Validate git-provider-url annotation

[ralphbean]

I ran into a case in the Fedora cluster where a user entered gitlab.com for their git-provider-url. Build-service processed this without a problem and passed it on to the PaC Repository. PaC accepted it no problem, but when it tried to operate on an incoming webhook, it failed hard because the url was missing its https:// prefix.

This is a request for build-service to start validating that annotation. If it doesn't conform to a url schema, the Component should be rejected from submission.

Related issue for PaC filed at openshift-pipelines/pipelines-as-code#1852