gRPC support

[andrewgryan]

Building on the RPC driver approach and using a more full-featured remote-procedure call framework I think a gRPC client/server needs to be shipped with FOREST to enable remote/local data visualisation.

# Build a gRPC service in a container, e.g. /rpc endpoint
forest service forest.config.yaml

# Build a Bokeh server with a gRPC client "driver"
forest ctl forest.config.yaml

This approach will allow multiple FOREST servers to connect together to share their datasets. By exposing replies to methods needed to populate glyphs and menus.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.