document how to generate vendor-agnostic SQL with sqlglot

[edublancas]

we just merged a big PR from @tonykploomber (#164) that will allow us to improve JupySQL compatibility across multiple SQL dialects. However, since we expect to keep adding features that run SQL queries on the user's behalf, we need to document how to do it.

Tony: please document your learning on using SQLglot for producing vendor-agnostic SQL queries so other contributors know how to do it.

[edublancas]

add it to the developer guide: https://jupysql.ploomber.io/en/latest/community/developer-guide.html

[tonykploomber]

Now we have a plan to drop sqlglot, this might not valid anymore
#307

[edublancas]

but we'll still keep (at least for now) for transpiling some internal queries. this is still useful but not urgent