Decryption trigger abstraction

[ezdac]

Currently, the sending of the Epoch decryption key-share by the keypers is triggered by receiving a gossipsub message DecryptionTrigger that functions as the collator-commitment.

We still want to keep that behaviour, but allow for different mechanisms to trigger sending the decryption key share. Abstracting this functionality would allow for different application logic (rollups, beacon chain integration) being used by the same codebase.

Different strategies to achieve this could be employed:

• HTTP API to trigger decryption across process-boundaries
• internal in-process abstraction layer:
  • different applications could plug-in code
  • code is part of the rolling-shutter source, different behaviour is switched during compile- or configuration time