Document configuring wasmCloud Host to use gRPC as the OpenTelemetry protocol

[joonas]

Capturing this as an item to do as it's top of mind:

Back in May, we added support for gRPC as an alternative for emitting OTEL signals, but it hasn't been captured in the Observability with OpenTelemetry docs as of yet, which in fact states the opposite:

Not all upstream options are supported—for example, the wasmCloud host does not support changing format to gRPC.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If this has been closed too eagerly, please feel free to tag a maintainer so we can keep working on the issue. Thank you for contributing to wasmCloud!

[joonas]

Not stale, we do still want this documented.