Specify formats of `spark.sql.session.timeZone`

There are two distinct types of ID (see https://docs.oracle.com/javase/8/docs/api/java/time/ZoneId.html):

1. Fixed offsets - a fully resolved offset from UTC/Greenwich, that uses the same offset for all local date-times
2. Geographical regions - an area where a specific set of rules for finding the offset from UTC/Greenwich apply

For example three-letter time zone IDs are ambitious, and depend on the locale. They have been already deprecated in JDK, see https://docs.oracle.com/javase/8/docs/api/java/util/TimeZone.html :

For compatibility with JDK 1.1.x, some other three-letter time zone IDs (such as "PST", "CTT", "AST") are also supported. However, their use is deprecated because the same abbreviation is often used for multiple time zones (for example, "CST" could be U.S. "Central Standard Time" and "China Standard Time"), and the Java platform can then only recognize one of them.

The ticket aims to specify formats of the SQL config spark.sql.session.timeZone in the 2 forms mentioned above.