Fetch mesh data on-demand in solution mode

[mkundu1]

Seems to be possible via the scheme function (stream-mesh-data-to-grpc-channel). We can have an rpc just to return the mesh data (can be streamed response).

Currently, mesh data is streamed via a "continous streaming" rpc.

We also need to get this working in solver mode.

[mkundu1]

Mesh data API future work (after PR #3618):
1. Properly support polyhedral connectivity. - Done
2. Support face zones (low-priority as already supported through other APIs).
3. Performance investigation: Some code can be moved from PyFluent to server (#3618 (comment)) - We don't need any change as of now.
4. Python API should take zone names alongwith ids. Add api to get allowed zone names. This basic API is in place, but we need to align it with other allowed values validations under field_data.
5. Pyfluent-visualization integration.
6. Add test and doc. - Add final doc after completing 4 above.