[IMP] add migration.yaml file to use during migrations

[david-banon-tecnativa]

Adds a new compose file (its getting a bit out of hand, now there are 4 of them!) to use during migrations
@pedrobaeza @josep-tecnativa
TT61263 @Tecnativa

[rrebollo]

@david-banon-tecnativa @pedrobaeza @josep-tecnativa Any hints on the recommended approach or examples for properly using this new migrations.yaml?

I use Doodba daily for migrations and have developed my own workarounds to handle the pain of maintaining one copier project per version. For example, small things like using global database and filestore volumes shared across versions that support the same PostgreSQL server (from v14 to v18 we can use PostgreSQL 13) to avoid the backup-restore cycle between versions.

However, looking at migrations.yaml, I don't fully understand it. What's the approach here? Any guidance would be greatly appreciated.

[david-banon-tecnativa]

This migrations.yaml file is mainly intended to separate the test instance from the migration instance, however at a template level ATM the only change is the domain being used.