devel/rubygem-strong_migrations61: New port

This gem catches the following unsafe migrations:

• adding a column with a non-null default value to an existing table
• changing the type of a column
• renaming a table
• renaming a column
• removing a column
• adding an index non-concurrently (Postgres only)
• adding a json column to an existing table (Postgres only)

Sponsored by: Nepustil