sql: add alias timezone for time zone session var #19440
Description
I tested using cockroach with postgresql_fdw from postgres and ran into this error:
ERROR: unknown variable: "timezone"
CONTEXT: Remote SQL command: SET timezone = 'UTC'
In pg docs it says that time zone is an alias for timezone
test=> SHOW timezone;
ERROR: unknown variable: "timezone"
test=> SHOW time zone;
time zone
-----------
UTC
(1 row)
in postgresql 10
test=# show timezone;
TimeZone
----------
UTC
(1 row)
test=# show time zone;
TimeZone
----------
UTC
(1 row)