Feature request: Support custom data migration template

[maria-lau]

It'd be nice if we could could designate a different data_migration template in our own repos to be used instead of the default found here:
https://github.com/ilyakatz/data-migrate/blob/master/lib/generators/data_migration/templates/data_migration.rb

[ilyakatz]

Hi there, to be frank, I'm not really adding any new features anymore. Happy to review the code/provide guidance if you're willing to give it a shot and create a PR

[bazay]

I've opened a PR implementing this functionality as it's something I was also interested in supporting, thanks.

[ilyakatz]

this has been added