Support mapping NodaTime's Interval to PG tsrange/tstzrange

[roji]

NodaTime's Interval type closely corresponds to PostgreSQL tsrange/tstzrange: both holds a start and end timestamp.

The interesting question is if this should be the default mapping (i.e. when reverse-engineering), or whether we should retain NpgsqlRange<DateTime> as the default.

We should also do this at the Npgsql ADO layer.

Suggested by @arontsang in https://github.com/npgsql/efcore.pg/issues/1607#issuecomment-768953160