Availability Subsystems: availability recovery subsystem

## Issue summary

- This subsystem is the inverse of the [Availability Distribution](https://github.com/ChainSafe/gossamer/issues/3598) subsystem: validators will serve the availability chunks kept in the availability store to nodes who connect to them. And the subsystem will also implement the other side: the logic for nodes to connect to validators, request availability pieces, and reconstruct the AvailableData.

## Sub Issues
- [x] Create a skeleton PR that would lead to smaller issues

## Other information and links

- polkadot-sdk link https://github.com/paritytech/polkadot-sdk/blob/2183669d05f9b510f979a0cc3c7847707bacba2e/polkadot/node/network/availability-recovery/src/lib.rs#L319
- node implementer's guide https://paritytech.github.io/polkadot-sdk/book/node/availability/availability-recovery.html