[gRPC] remote: add ability to specify array attributes in exported resources

[flxzt]

I was trying out the gRPC branch and noticed that certain attributes added to resources in my fork break when they are exported to the coordinator. The gRPC branch currently does not have support for array attributes.

This PR adds support for exactly that - (nested) array field attributes, by adding MapValueArray that contains repeated MapValue's to the .proto definition file and the conversion between config dicts <-> grpc messages.

I know the gRPC branch is still very much in movement, but I hope the PR will be considered. It improves the expandability of the framework in forks and closes the feature gap to the old crossbar implementation