fetch sqlite databases from object storage

[vrongmeal]

Description

#2568 (comment)

[tychoish]

as I was thinking about this, we might be fine to not have a size limit here: we don't have a size limit for any other kind of file, and say, JSON (non-new-line) and excel would all run into size limits in the same way (parquet and csv and ndjson and bson can all be streamed), so we might as well just download whatever now and solve the limited space issue separately.

[talagluck]

Beyond just being able to hit this in object storage from one of the major cloud providers, it would be nice to access this anywhere it's available, e.g. GitHub:

CREATE EXTERNAL DATABASE census_names
FROM sqlite
OPTIONS (
location = 'http://2016.padjo.org/files/data/starterpack/census/census2000names.sqlite',
);

[tychoish]

I think it makes sense to just use tempfiles tied to the lifetime of the SQLite Access object: if we get something that isn't a pathbuf, download it, write it to the tempfile and then go from there as "normal."

Need to take extra care to avoid writing to these temporary databases.

If/when we add support for COPY TO we'll just have to be careful to restrict support there too.

[talagluck]

How would that interact with the INSERT INTO feature just added in #2745?

[tychoish]

We'd have to prevent inserts in these cases