Prepare note and discussion GraphQL types for abuse report

What does this MR do and why?

This is a preparation for exposing abuse report notes. I already opened that MR but it got really big and still has some issues that have to be fixed so I decided to create this one to keep the scope smaller.

this MR:

• creates base interfaces for note and discussion types that can be reused
• use these interfaces for existing notes and discussions
• create new types for note and discussion on abuse reports

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

No changes in the UI

How to set up and validate locally

Run the graphql query to make sure we didn't break anything for existing notes, eg.:

{
  issue(id: "gid://gitlab/Issue/56") {
    id
    discussions {
      nodes {
        id
        replyId
        notes {
          nodes {
            id
            body
          }
        }
      }
    }
    notes {
      nodes {
        id
        body
        bodyHtml
      }
    }
  }
}