This patch adds a new time_bucket_gapfill function that
allows bucketing in a specific timezone.
You can gapfill with explicit timezone like so:
`SELECT time_bucket_gapfill('1 day', time, 'Europe/Berlin') ...`
Unfortunately this introduces an ambiguity with some previous
call variations when an untyped start/finish argument was passed
to the function. Some queries might need to be adjusted and either
explicitly name the positional argument or resolve the type ambiguity
by casting to the intended type.
b34b91f18b