Log request protobuf msg size

[jianoaix]

Why are these changes needed?

The serialized protobuf message is the actual amount of data to be transmitted. And it could be quite different than the accounting in golang.

Example:
2024-05-23 16:14:12.845 | {"time":"2024-05-23T23:14:12.845549648Z","level":"DEBUG","source":{"function":"github.com/Layr-Labs/eigenda/disperser/batcher/grpc.(*dispatcher).sendChunks","file":"/app/disperser/batcher/grpc/dispatcher.go","line":134},"msg":"sending chunks to operator","component":"Dispatcher","operator":"18.218.243.40:32005;32004","size":2689920,"request message size":10682225}

Checks

• I've made sure the lint is passing in this PR.
• I've made sure the tests are passing. Note that there might be a few flaky tests, in that case, please comment that they are not relevant.
• Testing Strategy
  • Unit tests
  • Integration tests
  • This PR is not tested :(

[pschork]

I'll include it in the release.