Refactor external dependencies to be always encapsulated

[areknoster]

Currently some dependencies seem to be spread across PDCL components - e.g. FirstToLastConsumer is coupled with IPNS. Instead, those kind of dependencies should be designed as logical unit, that's hidden behind an interface and can have multiple implementations.

In particular following changes could be introduced:

• IPNS should implement thead interfaces and no component should depend on it directly
• ratelimiting should be a part of grpc package
• CID should be agnostic to IPFS implementation

Worth discussing: should proto be somehow abstracted away?