Show prebuild configuration state on the project prebuilds page

Problem to solve

Currently, when removing (or reconfiguring) the GitHub app or removing the GitLab webhook the project, there's no feedback to the user the GitHub app needs to be reconfigured or the webhook is missing. See also https://github.com/gitpod-io/gitpod/issues/7009.

(Revised) Proposal

From comment

MVC to help users understand the understand the state of a prebuild configuration for a specific project:

Could we show a repository prebuild configuration status on /projects/<project-name>/prebuilds with one of the states below?

Prebuild configuration states

Any repo

• OK - last webhook received at <date/time> for <event type>
• No prebuild configured for this repo (no prebuild in gitpod.yml - file or db)

GitHub

• Gitpod app on GitHub not installed for org or user <name>
• Gitpod app on GitHub not configured to access <repo>

Other git integrations

• No webhook installed for <repo> (is this possible to detect?)

cc: @gtsiolis

Start at the /projects//prebuilds page and review issue 7009 for related context. Map the available prebuild configuration states for GitHub and other integrations, then confirm that the page gives appropriate feedback for each state described in the proposal.