GraphQL: Filter by access_levels in projects members

What does this MR do and why?

Filter by access_levels in projects members GraphQL API

Closes #541386 (closed)

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create a project named test-project inside group test-group
2. Visit http://localhost:3000/-/graphql-explorer

Query:

query projectOwners {
  project(fullPath: "test-group/test-project") {
    projectMembers(accessLevels: OWNER) {
      nodes {
        user {
          username
        }
      }
    }
  }
}

Response:

{
  "data": {
    "project": {
      "projectMembers": {
        "nodes": [
          {
            "user": {
              "username": "root"
            }
          }
        ]
      }
    }
  },
  "correlationId": "random"
}

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