Add members to project graphQL endpoint

What does this MR do?

It adds the project members information to the project graphQL endpoint.

Usage Example

Request

{
  project(fullPath: "flightjs/flight") {
    name
    projectMembers {
      edges {
        node {
          id
          accessLevel
          user {
            id
            username
            name
          }
        }
      }
    }
  }
}

Response

{
  "data": {
    "project": {
      "name": "Flight",
      "projectMembers": {
          {
            "node": {
              "id": "gid://gitlab/ProjectMember/53",
              "accessLevel": 30,
              "user": {
                "id": "gid://gitlab/User/13",
                "username": "sherril",
                "name": "Scarlet Gleichner"
              }
            }
          }
...

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Related issue: #216145 (closed)