Add a --cli flag to Seafowl, which would allow running an interactive line editor locally.

This is mainly for quicker prototyping/troubleshooting/testing, as currently all the alternatives are sub-optimal:

• the HTTP frontend usually requires formatting curl request which introduces some friction, as it's mostly devised to be used in production settings (+ it doesn't support all types atm, e.g. see Result JSON unsupported types #393)
• the PG frontend doesn't support the full Seafowl syntax for now
• there is also the one-off command, but it only runs one query and exits