Add graphql query for project secrets manager

This is the 3rd part of #469580 (closed) where we add the GraphQL query for project secrets manager. Frontend will use this to poll for the status of the secrets manager while provisioning.

Sample query to run as project owner:

query {
  projectSecretsManager(projectPath: "test-parent-group/test-sub-group/test-project-sub-group") {
    status
    project {
      id
    }
    ciSecretsMountPath
  }
}

response:

{
  "data": {
    "projectSecretsManager": {
      "status": "PROVISIONING",
      "project": {
        "id": "gid://gitlab/Project/57"
      },
      "ciSecretsMountPath": "project_57/ci"
    }
  }
}