Add ALL filter to cluster agent query

Issue: Update organization cluster agents query to acc... (#545224 - closed)

What does this MR do and why?

This MR adds a new filter ALL to the workspacesClusterAgents query, that will return all cluster agents belonging to the given namespace (organization or group). This is to simplify the handling of pagination in the frontend, see Workspaces Cluster Agents Admin Settings UI (#545241 - closed).

The AVAILABLE and UNMAPPED filters are also removed:

• Due to product's decision to only return agents that have workspaces enabled in their configuration within the organization's workspacesClusterAgents field, AVAILABLE is removed in favour of DIRECTLY_MAPPED as they now serve the same function.
• There is no current use case for the UNMAPPED filter.

References

• Update organization cluster agents query to acc... (#545224 - closed)

Screenshots or screen recordings

Org	Group

How to set up and validate locally

• Pull this branch and visit the GQL explorer in your GDK: /-/graphql-explorer

• Run the following queries:

  • Organization:

    # Query:
    query organizationWorkspacesClusterAgentsQuery(
      $organizationId: OrganizationsOrganizationID!
    ) {
      organization(id: $organizationId) {
        workspacesClusterAgents(
          filter: ALL
        ) {
          nodes {
            id
            name
          }
        }
      }
    }
    
    # Variables:
    {
      "organizationId": "gid://gitlab/Organizations::Organization/1"
    }

• Group:

  # Query
  query getRemoteDevelopmentClusterAgents($namespace: ID!) {
    namespace(fullPath: $namespace) {
      id
      remoteDevelopmentClusterAgents(filter: ALL) {
        nodes {
          id
          name 
        }
      }
    }
  }
  
  # Variables
  {
   "namespace": "gitlab-org"
  }

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