Monitor Implementation

[liamsi]

Sub-tasks:

• define monitor services/protos
• grpc client for querying the GetMutations API
• implement mutations polling
• store latest observed SMR
• MVP monitor binary
• add Dockerfile with binary as entry-point
• add service to docker-compose.yml for local tests
• call / implement verification methods
• add kubernetes configuration
• document possible errors in markdown document (see WIP: minimalistic Monitor  #709 (comment))
• publish monitor IP as a service (depends on above steps)
• add prometheus vars to monitor