Add alias rake task for db:* defined by actual schema

[ka8725]

Currently "db:phantom_migrations" rake task is defined in "db" namespace, but other are in actual_db_schema namespace. That's inconsistent and might lead to confusion. So this grep shows no all tasks from actual_db_schema:

$ rails -T | grep actual

rails actual_db_schema:delete_broken_versions[versions,database]                 # Delete broken migration versions from the database
rails actual_db_schema:diff_schema_with_migrations[schema_path,migrations_path]  # Show the schema.rb diff annotated with the migrations that made the changes
rails actual_db_schema:install                                                   # Install ActualDbSchema initializer and post-checkout git hook
rails actual_db_schema:install_git_hooks                                         # Install ActualDbSchema post-checkout git hook that rolls back phantom migrations when switching branches

Make sure all rake tasks defined by the gem are also defined in actual_db_schema namespace. For back compatibility, please do not remove the tasks from their namespaces defined before - make only aliases.