Improve batched background migration generator

What does this MR do and why?

This MR improves our batched background migration generator to be more user-friendly and support EE-only migrations

Before

bin/rails g batched_background_migration
Usage:
  rails generate batched_background_migration:batched_background_migration NAME [options]

Options:
  [--skip-namespace], [--no-skip-namespace]              # Skip namespace (affects only isolated engines)
  [--skip-collision-check], [--no-skip-collision-check]  # Skip collision check
  [--table-name=TABLE_NAME]                              # Indicates when to generate table name
  [--column-name=COLUMN_NAME]                            # Indicates when to generate column name
  [--feature-category=FEATURE_CATEGORY]                  # Indicates when to generate feature category

Runtime options:
  -f, [--force]                    # Overwrite files that already exist
  -p, [--pretend], [--no-pretend]  # Run but do not make any changes
  -q, [--quiet], [--no-quiet]      # Suppress status output
  -s, [--skip], [--no-skip]        # Skip files that already exist

Description:
    Generates files required for batched background migration.

Example:
    rails g batched_background_migration my_batched_migration --table_name=users --column_name=id --feature_category=gitaly

    This will create:
        db/post_migrate/20230213215230_queue_my_batched_migration.rb
        spec/migrations/20230213215230_queue_my_batched_migration_spec.rb
        lib/gitlab/background_migration/my_batched_migration.rb
        spec/lib/gitlab/background_migration/my_batched_migration_spec.rb
        db/docs/batched_background_migrations/my_batched_migration.yml

After

$ bin/rails g batched_background_migration
Usage:
  rails generate batched_background_migration:batched_background_migration NAME [options]

Options:
  [--skip-namespace], [--no-skip-namespace]              # Skip namespace (affects only isolated engines)
  [--skip-collision-check], [--no-skip-collision-check]  # Skip collision check
  --table-name=TABLE_NAME                                # Table from which records we will be batching
  --column-name=COLUMN_NAME                              # Column to use for batching
                                                         # Default: id
  --feature-category=FEATURE_CATEGORY                    # Feature category to which this batched background migration belongs to
  [--ee-only], [--no-ee-only]                            # Generate files for EE-only batched background migration

Runtime options:
  -f, [--force]                    # Overwrite files that already exist
  -p, [--pretend], [--no-pretend]  # Run but do not make any changes
  -q, [--quiet], [--no-quiet]      # Suppress status output
  -s, [--skip], [--no-skip]        # Skip files that already exist

Description:
    Generates files required for batched background migration.

Example:
    rails g batched_background_migration my_batched_migration --table_name=users --column_name=id --feature_category=gitaly

    This will create:
        db/post_migrate/20230213215230_queue_my_batched_migration.rb
        spec/migrations/20230213215230_queue_my_batched_migration_spec.rb
        lib/gitlab/background_migration/my_batched_migration.rb
        spec/lib/gitlab/background_migration/my_batched_migration_spec.rb
        db/docs/batched_background_migrations/my_batched_migration.yml

Generating an EE-only batched background migration

bin/rails g batched_background_migration mysupereeonlymigration --ee-only --table_name=users --column_name=id --feature_category=gitaly
      create  db/post_migrate/20230613215917_queue_mysupereeonlymigration.rb
      create  spec/migrations/20230613215917_queue_mysupereeonlymigration_spec.rb
      create  ee/lib/ee/gitlab/background_migration/mysupereeonlymigration.rb
      create  lib/gitlab/background_migration/mysupereeonlymigration.rb
      create  ee/spec/lib/ee/gitlab/background_migration/mysupereeonlymigration_spec.rb
      create  db/docs/batched_background_migrations/mysupereeonlymigration.yml

Further work

I am not sure why but the file under spec/migrations/<timestamp>_queue_<migration_name>_spec.rb doesn't get removed when you call bin/rails d batched_background_migration

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.