listen to parentchain events

[brenzi]

• Feed in all events from one block into enclave
• Validate storage proof for system pallet events
• Allow subscription for particular event

[clangenb]

Connected to: #1208

[coax1d]

For bullet point 3 in this issue there is really a couple approaches and it is worth discussing an approach.

For now regarding bullet points 1 & 2 simply query the ParentChain for both the events and the events_storage_proof pass those into the enclave when syncing the ParentChain blocks and validate the proof.

Now once we have the validated events we can do the simplest approach and least robust approach that would solve #1208 and #970 which is:
Pass the validated events along with the blocks to the import dispatcher

worker/enclave-runtime/src/lib.rs

Line 380 in 5fe663b

import_dispatcher.dispatch_import(blocks_to_sync)?;

However this is not really achieving being able to subscribe to a particular event that is mentioned in bullet point 3.

A solution to achieve this may be to have some temporary storage of events in the enclave which can be indexed by a particular block hash. This way we can allow someone to query the validated events for a particular block and then search those events for what they are looking for i.e. (Extrinsic success, or Extrinsic Failed, Certain Pallet events etc.) Or to even subscribe to a particular validated event and just listen for when it occurs given the current ParentChain block.

This is the solution I am leaning towards which would allow for subscription.

Open to any feedback.

[coax1d]

Closed by #1272