Add top-level `groups` GraphQL query

What does this MR do and why?

Adds a top-level GraphQL groups query type that supports a name search argument search.

The security policy editor will use the query type to search for groups accessible to the user. Currently, the List Groups API endpoint is used. As part of #378234 (closed), the frontend will start using the existing Group.descendantGroups query, depending on an application setting. To avoid having to conditionally call the GraphQL or REST API, this MR introduces the GraphQL equivalent of the List Groups API endpoint.

How to set up and validate locally

{
  groups(search: "win") {
    nodes {
      name
      fullPath
    }
  }
}

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #378234 (closed)