feature request: baml-cli dev --playground (or something similar)

[sxlijin]

For folks who don't use VSCode, we need a way to provide them with a decent developer experience.

The most likely path forward for this will be to allow users to spin up a local version of promptfiddle.com, backed by their local filesystem, something like

baml-cli dev --playground [port-number]

This will allow people to not have to download, install, and configure VSCode to edit their BAML code.

We've had a few requests from non-VSCode users about something along these lines: see #932 and #889