Use parameterized templates in migrations

[kriswuollett]

Is your feature request related to a problem? Please describe.

Want to host multiple copies of the same app, possibly for multi-tenancy, in the same database for cloud cost savings.

Describe the solution you'd like

• support template files from handlebars-rust auto-detected with .hbs file extension
• add a --data parameter to the cli to pass the json data context
• add sql-related handlebars helpers to make sure things like identifiers are correct

Describe alternatives you've considered

Keep migrations in alembic.

Additional context

Also need migration table renaming to land, see #1698.