This PR extends pipeline expressions to allow converting from a Query to a Pipeline expression. All necessary stages and expressions have been added

All existing system tests have been updated to run both as a query, and as a pipeline

Note:

• most of the changes in the PR is relatively boiler plate. pipeline_stages and pipeline_expressions have some new classes. But the main change to review is base_query.pipeline(), which implements the conversion from query to pipeline format

TODO: use enterprise mode for system tests