Add admin_show_path and admin_edit_path GraphQL fields

What does this MR do and why?

Related to #560248 (closed)

Currently we are building URLs for admin area group/project lists on the frontend - app/assets/javascripts/admin/groups/index/constants.js#L47

This isn't ideal and can lead to bugs, it is better to use the backend as SSOT for URLs.

This MR exposes admin_show_path and admin_edit_path fields on Group and Project GraphQL fields so they can be used on the frontend.

Screenshots or screen recordings

As an admin

As a non-admin

How to set up and validate locally

1. Sign in as an admin
2. Go to /-/graphql-explorer
3. Run the following query

{
  adminGroups(first: 2) {
    nodes {
      ... on Group {
        fullName
        adminShowPath
        adminEditPath
      }
    }
  }
  adminProjects(first: 2) {
    nodes {
      ... on Project {
        nameWithNamespace
        adminShowPath
        adminEditPath
      }
    }
  }
}

1. Go to /admin/users and impersonate a regular user
2. Run the GraphQL query again, adminShowPath and adminEditPath should be null.

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