Protobuf migration

[donaldthibeau]

Requirements

• Maintain protobuf as a standalone repo as a single source of truth. This makes it easier to consume via embedding withinn broader services repo.
• Set one tag for the protobuf repo which automates update to preview net and a second tag which updates to locations like maven.
• This will allow for both single source of truth as well as the ability to push into more consumable locations.

Decision 1/7/2021:

• The hedera-protobuf repo will be used as the single source of truth for all hedera protobuf files including HAPI and mirror node
• This allows the aggregation of multiple components, independent reviews not tied to services code, and accessible for all languages
• hedera-services repo will reference the hedera-protobuf repository for protobufs and will not be referenced within the hedera-services repo

TODO:

• Proposal on the structure of the hedera-protobuf repo for both HAPI and mirror node protobufs