sqlmigrate should accept migration file path as single argument

[Hendrik Richter]

Currently, after running makemigrations, the output shows the migration file path:

Migrations for 'invoices':
invoices/migrations/0022_alter_invoice_country_code.py
        - Alter field country_code on invoice

To use sqlmigrate, I need to manually split this into two arguments:

./manage.py sqlmigrate invoices 0022_alter_invoice_country_code

It would be more convenient if sqlmigrate also accepted the path directly to make copy and pasting it easily possible:

./manage.py sqlmigrate invoices/migrations/0022_alter_invoice_country_code.py

Similarly, migrate --plan outputs a dotted format:

Planned operations:
invoices.0022_alter_invoice_country_code
    - Alter field country_code on invoice

It would be convenient to use this directly as well:

./manage.py sqlmigrate invoices.0022_alter_invoice_country_code

Proposal:
Make migration_name optional. When only one argument is provided, parse app_label and migration_name from it, supporting both the path format (app/migrations/name.py) and the dotted format (app.migration_name).