GraphQL: Add systemId argument to `CiRunner.managers`

What does this MR do and why?

This MR adds a systemId argument to CiRunner.managers. This is a step to get GraphQL parity with the REST API endpoint parameter being added in !140667 (merged).

Changelog: added

Part of #438005

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

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. As admin, create a runner in http://gdk.test:3000/admin/runners (New instance runner button)

2. Ensure Run untagged jobs is checked and click Create runner

3. Follow the instructions to register the runner (gitlab-runner register)

4. Start the runner (gitlab-runner run)

5. Run the following query in http://gdk.test:3000/-/graphql-explorer, replacing the value in systemId with the contents of your ~/.gitlab-runner/.runner_system_id file:

   {
     runners(creatorId: "gid://gitlab/User/1") {
       nodes {
         id
         description
         version
         managers(systemId: "s_c2d22f638c25") {
           nodes {
             id
             systemId
           }
         }
       }
     }
   }

The query should return the runner you just registered, along with the runner manager. If you change the systemId to some other value, the runners.nodes[].managers.nodes[] collection should come out empty.

Database query plans

Ci::RunnerManager Load ↳ app/models/preloaders/runner_manager_policy_preloader.rb:16:in `execute'

https://console.postgres.ai/gitlab/gitlab-production-ci/sessions/25102/commands/79736

SELECT "ci_runner_machines".*
FROM "ci_runner_machines"
WHERE "ci_runner_machines"."runner_id" IN (/*100 runner ids*/)
  AND "ci_runner_machines"."system_xid" = 's_096156a6a024'
ORDER BY "ci_runner_machines"."id" DESC

 Sort  (cost=196.95..196.96 rows=1 width=100) (actual time=48.854..48.873 rows=101 loops=1)
   Sort Key: ci_runner_machines.id DESC
   Sort Method: quicksort  Memory: 39kB
   Buffers: shared hit=303 read=107 dirtied=13
   I/O Timings: read=4.922 write=0.000
   ->  Index Scan using index_ci_runner_machines_on_runner_id_and_system_xid on public.ci_runner_machines  (cost=0.42..196.94 rows=1 width=100) (actual time=0.678..48.691 rows=101 loops=1)
         Index Cond: ((ci_runner_machines.runner_id = ANY ('{/*100 runner ids*/}'::bigint[])) AND (ci_runner_machines.system_xid = 's_096156a6a024'::text))
         Buffers: shared hit=300 read=107 dirtied=13
         I/O Timings: read=4.922 write=0.000

Ci::Runner Load ↳ app/models/preloaders/runner_manager_policy_preloader.rb:16:in `execute'

https://console.postgres.ai/gitlab/gitlab-production-ci/sessions/25102/commands/79737

SELECT "ci_runners".*
FROM "ci_runners"
WHERE "ci_runners"."id" IN (/*100 runner ids*/)

 Index Scan using ci_runners_pkey on public.ci_runners  (cost=0.43..347.45 rows=101 width=271) (actual time=19.644..520.582 rows=101 loops=1)
   Index Cond: (ci_runners.id = ANY ('{/*100 runner ids*/}'::integer[]))
   Buffers: shared hit=299 read=110 dirtied=21
   I/O Timings: read=481.284 write=0.000