List all project secrets (Backend)

This is the backend issue for listing project secrets.

Frontend issue: #470373 (closed)

Design

What should be done here

• GraphQL resolver for listing project secrets.
  • Take into account the permissions defined by the user in #470366 (closed). If the current user's role is not allowed "Access" to secrets, the request should be denied.
  • No Pagination (see #470372 (comment 2248728895))