This change adds a repository form view for GitHub that modifies the form when a GitHub App installation account is selected. When an app installation is selected for the account, this restricts the available plans to just the new app plan, and shows only the "Repository Name" field. This also labels accounts so app installation accounts and PAT-based accounts that have the same username can be distinguished. Testing Done: - Used the repository form for GitHub repos that were on both app-install and PAT linked hosting service accounts. Verified that interaction worked as expected. - Ran unit tests