Add GRPC message definitions for sending metadata requests and receiving metadata from worker

[anandagopal6]

Need to add new message definitions to FunctionRpc.proto to enable the worker indexing workflow.

Messages to add:

• Message for host requesting metadata from worker; should send directory path
• Message for sending metadata from worker to host; should include list of metadata + status results and an overarching status result for the overall request
• Message including all necessary information to populate FunctionMetadata; each function will correspond to one of these messages, so a list of these messages will be sent through the overall response message from worker to host

[anandagopal6]

Still need to add the StatusResult field for the overall metadata response message and integrate this into the response parsing logic.

[anandagopal6]

StatusResult field has been added. Message types should be fully implemented now.

[fabiocav]

Work is in progress, expecting a PR in 106. Updating sprint assignment to reflect that