`ext/` folder containing import helpers for common extensions

[eliassjogreen]

An idea I had was to create an ext/ folder which contains helpers using plug for downloading and importing common extensions such as spatialite and the sqlean extension pack. This might be out of the scope of this repo or module and may be better off as it's own thing, especially considering these extensions may need to be built in the CI (sqlean already has binaries in it's repo, but spatialite would need building) but there are also ergonomic and ease-of-use benefits of keeping them here.

[DjDeveloperr]

IMO these extensions should be a separate module. I'd want to keep only the core SQLite in this module to keep the maintenance burden balanced.