feat(proto): fix missing timezone parameter in timestamp translation

[rtpsw]

See #181

[rtpsw]

@cpcloud, it looks like commitlint fails due to checking more than just the last commit message, which I thought would be the one to be selected in the eventual squashing. How to handle this error?

[cpcloud]

This looks like a custom extension to substrait and a modification of the spec outside of the main substrait-io/substrait repo.

Regarding the actual change, the TimetampTZ type is intentionally without a timezone. It only indicates that there is a timezone. The design is similar to the way time zones work in most relational databases like postgres (see https://www.postgresql.org/docs/current/datatype-datetime.html#DATATYPE-TIMEZONES).

That said, unlike postgres there's nothing documented in substrait saying that a TimestampTZ is assumed to be UTC so we should nail that down.

[rtpsw]

Thanks, I wasn't aware that spec changes need to go to substrait-io/substrait.

Given TimezoneTZ does not carry a timezone, how should a timezone value be represented within a Substrait plan? I think such a timezone value is needed for casting of a time-string to a specific timezone. Currently, in related Arrow code, I see a default timezone value is used.

I'm OK with canceling this PR if the conclusion is that a timezone value is not needed and only the Substrait docs need to be fixed.

[rtpsw]

@cpcloud - ping. See question here.

[cpcloud]

@rtpsw Is there a use case you have that requires a change to the substrait spec? If so, let's discuss in the substrait-io repo and close this PR out! Thanks!

[rtpsw]

Created substrait-io/substrait#190 for the discussion.