probe: use postgres instead of sqlite when enabled

[3nprob]

trafficstars

If clightning is already configured to use a postgres database, it would be great to create a table there, that rather than creating a new sqlite3 database on disk

Especially for setups where the datadir for clightning is on a network-attached volume/disributed filesystem, as sqlite is known to be prone to corruption in those scenarios

[cdecker]

Adding postgresql support, or really any db supported by sqlalchemy should be very easy. I'd add a --probe-db option to allow operators to specify where to store the results, rather than hijacking the existing --wallet option, since that might be unexpected.

Very good suggestion 👍