feat: [Executor-client] Passthrough logic for migration

[eleonoradgr]

What changed?

• Implemented the logic for the migration:
  • no heartbeating if local passthrough
  • no assignment if local passthrough shadow
  • assignment in case of distributed passthrough and onboarded
• logic for consistency checks and metrics in case passthrough shadow and distributed passthrough
• static configuration to control the first step of the migration

Why?
These mechanism are needed to migrate incrementally from using sharding logic which is part of the system to the shard distributor

How did you test it?
unit tests and local testing

Potential risks
nothing is onboarded yet, except canary service

Release notes

Documentation Changes