Document how to bulk import from GitHub in RHDH

General Flow 

• Prompt user for an organization or user (support for multiple can be added in the future)
  • List all repositories in the given organization or user that the github apps have access to.
  • Allow the user to select a subset of the repositories
• Generate a catalog-info.yaml for each repository based on provided information and open a PR to add it into the repository
  • We will want the admin user to be able to customize this catalog-info.yaml with things like annotations, owners, etc.
  • We should have a default catalog-info.yaml if no additional configurations were provided
  • A dryrun catalog ingestion should occur to determine if any entity name collisions occur.
    • Import shouldn't fail, so something like a -(number) may need to be appended to the end of the entity name to ensure uniqueness
    • Sanitation of inputs will also be required to follow the backstage naming schemas. 
• Initial implementation won't do tracking of import status (ex: Waiting for PR Approval) and will operate on a Fire and Forget basis
  • We will still want to track whether the PR was created properly and if the generated catalog-info.yaml was valid and track those failures if they occur

Acceptance Criteria

1. As a platform engineer, I want to give permission to specific users/groups to use the bulk import plugin using RBAC
2. As a platform engineer, I want to provide a template of the `catalog-info.yaml` that will be used by the bulk import plugin
3. As a developer, I want to be able to bulk import my existing applications available in Git (GitHub, GitLab, etc.).
4. As a developer, I should import only the repositories I have access to. I cannot import someone else repo.
5. As a developer, when I import a Git repo, it should create a PR with the catalog-info.yaml and add the component to the catalog.
6. It would be great that the process is using a software template. The platform engineer will be able to provide the catalog-info file and define the various steps. Create the PR, submit a ServiceNow ticket, send a notification, add to the catalog, or anything else.

See more details in feature request: RHIDP-834

For reference, see: https://docs.google.com/document/d/1lXAO7NshemNd21EMpUWtDPNMrm5uEhqBLr-rLWen1eM/edit?usp=sharing