Implement feature-flagged GraphQL end-point for data transfer monitoring

What does this MR do and why?

Epic: Expose transferred git (egress) data via API (&9330) Problem

We don't have a public API to expose the transferred data. Requirements Design of the page

Design a new Transfer Page (#355976)

Screenshots or screen recordings

this is are the fields that we introduced to the schema.

For projects:

query ProjectDataTransfer {
  project(fullPath: "gnuwget/Wget2") {
    dataTransfer { # ProjectDatatransferType
      totalEgress # BigInt
      egressNodes { # EgressNodeType.connection_type
        nodes {
          date # String
          totalEgress # BigInt
          repositoryEgress # BigInt
          artifactsEgress # BigInt
          packagesEgress # BigInt
          registryEgress # BigInt
        }
      }
    }
  }
}

For groups:

query ProjectDataTransfer {
  group(fullPath: "gnuwget") {
    dataTransfer { # ProjectDatatransferType
      egressNodes { # EgressNodeType.connection_type
        nodes {
          date # String
          totalEgress # BigInt
          repositoryEgress # BigInt
          artifactsEgress # BigInt
          packagesEgress # BigInt
          registryEgress # BigInt
        }
      }
    }
  }
}

How to set up and validate locally

1. Enable the the feature-flag

   Feature.enable(:data_transfer_monitoring)

2. go to graphql-explorer http://127.0.0.1:3000/-/graphql-explorer
3. try the queries above

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #383773