Annotation edgedb version that generates migration

[tailhook]

At the start of migration add:

# Generated by EdgeDB version: v3.0-alpha.2

Then, when reading migrations do two things:

1. Warn if current edgedb version is lower than that
2. If migration cannot be applied, add the check to context of the error kinda:

ScheamDefinitionError: something gone wrong
[..100 lines of error descripiton..]
Note: the migration created by EdgeDB v3.0-alpha.2, current EdgeDB is v2.12