Collect CCMs from the events for Chain connector plugin

[ishantiw]

Description

We need to collect CCMs in order to select them and create CCU transaction to send it over to another chain. Currently, we don't have mechanism to collect CCMs.

• Listen to events (name of event TBD) related any new ccm being added to the outbox of mainchain.
• Add handler for the event where we store these CCMs
• In cleanup function, remove all the CCMs before lastCertifiedHeight

Acceptance Criteria

• Should have unit test for the event listener for new events related to CCM
• Should have unit test for the CCM handler
• Should have unit test for cleanup function for CCMs

Additional Information