This fixes three issues identified in the predefined migration for postgres v2-v3

relation already exists

Can error with the following:

{
  err: [DatabaseError],
  msg: 'Error running migration 20250502_020052_relationships_v2_v3 column "relation_id" of relation "table_name" already exists.'
}

This was happening when you run a migration with both a required relationship or upload field and no schema specified in the db adapter. When both of these are true the function that replaces ADD COLUMN and ALTER COLUMN in order to add NOT NULL constraints for requried fields, wasn't working. This resulted in the ADD COLUMN statement from being being called multiple times instead of altering it after data had been copied over.

camelCase column change

Enum columns from using select or radio have changed from camelCase to snake case in v3. This change was not accounted for in the relationship migration and needed to be accounted for.

DROP CONSTRAINT

It was pointed out by here that the DROP CONSTRAINT needs to include IF EXISTS so that it can continue if the contraint was already removed in a previous statement.

fixes #10162