Doc: implement grpc properties as both parameter and attribute

In #265, we're adding a `doc` parameter to the `grpc_data_property` wrappers, to set the docstring on the properties. However, to avoid duplication of the docstring itself it's only set on read-only properties (where the same information doesn't need to be specified in the `Parameters` section of the `__init__` docstring.

We should find a way to de-duplicate this information while still documenting it both on the property itself, and in the `Parameters`. Probably, the `Parameters` section can be auto-generated from the property docstrings.

Start with the grpc_data_property wrappers and the documentation changes described in #265, then inspect how property docstrings and the __init__ Parameters section are currently generated. The work is done when one source of documentation produces both the property documentation and matching parameter entries without duplicating the docstring text.

Written by the indexing model from the issue text.