cubicweb #5450566 Allow use of migration script before tables are created [open]

This script would allow for add extensions before the schema is initialized.

For example, it would allow to enable Postgis extension before a schema using Geometry attribute is created in database.

This would also be a great place to add new languages to Postgres.

done in<not specified>
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patchAdd new migration script to install db addons before schema init. [rejected]