Epic: Productize Continuous Migration

[mkysel]

This is a continuation of #885

The acceptance criteria are as follows:

• mainnet migration (pre-seed) is fully complete
• sync and indexer are fully caught up
• all processes can keep up with continuous migration

Additionally we need to build:

• measure delay between V3 publish and availability in d14n
• alerts and monitoring in case continuous migration falls behind

This might expose additional issues such as #1503 that will need fixing.