Description:
    Generates new database indices

    If no --database option is specified, uses the default database.

Example:
    rails generate nandi:index table_name index_col

    This will create:
        db/safe_migrations/20190424123727_add_index_on_index_col_to_table_name.rb

    or

    rails generate nandi:index table_name_1,table_name_2 index_col

    This will create:
        db/safe_migrations/20190424123727_add_index_on_index_col_to_table_name_1.rb
        db/safe_migrations/20190424123728_add_index_on_index_col_to_table_name_2.rb

    or

    rails generate nandi:index table_name index_col_1,index_col_2

    This will create:
        db/safe_migrations/20190424123727_add_index_on_index_col_1_index_col_2_to_table_name.rb

    or

    rails generate nandi:index table_name index_col --index_name bespoke_idx_name

    This will create:
        db/safe_migrations/20190424123727_add_index_on_index_col_to_table_name.rb
    with the specified bespoke index name

Multi-database examples:
    rails generate nandi:index users email --database primary
        creates index migration in primary database directory

    rails generate nandi:index events created_at --database analytics
        creates index migration in analytics database directory
