Add :timezone key to database metadata (#36413)

* Add timezone to database metadata

* Use UTC as _user timezone_ for snowflake driver

* Use user timezone as db-default-timezone

* Update oracles unprepare-value to handle Z UTC

* Update `driver/db-default-timezone :h2` to use jvm timezone

* Update containers timezone to match instance timezone and tests

* Update modules/drivers/oracle/src/metabase/driver/oracle.clj

Co-authored-by: metamben <103100869+metamben@users.noreply.github.com>

* Make unprepare symmetric for offset and zoned datetime

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Co-authored-by: metamben <103100869+metamben@users.noreply.github.com>