[fan-out integration] Record triggered integrations and results

[migmartri]

Operators can attach integrations to their workflows, this means that these integrations will get triggered when an attestation is received.

The problem with the current implementation is that there is not actual paper trail of the 1) execution of the integration and 2) its result.

We should store in the DB a new entity, i.e integrationEvents associated with workflowRun that will contain the different immutable events of when an integration was queued, in-progress or finished with or without error and an optional result struct.

This will allow us to show such events in chronological order, enable async processing and events replay in the future and so on.

Recording the result is a potential prerequisite for #122

See #39 for more information about the global effort on improving integrations firing logic.