### What changes were proposed in this pull request?
In the PR, I propose to update the doc for the `timeZone` option in JSON/CSV datasources and for the `tz` parameter of the `from_utc_timestamp()`/`to_utc_timestamp()` functions, and to restrict format of config's values to 2 forms:
1. Geographical regions, such as `America/Los_Angeles`.
2. Fixed offsets - a fully resolved offset from UTC. For example, `-08:00`.
### Why are the changes needed?
Other formats such as three-letter time zone IDs are ambitious, and depend on the locale. For example, `CST` could be U.S. `Central Standard Time` and `China Standard Time`. Such formats have been already deprecated in JDK, see [Three-letter time zone IDs](https://docs.oracle.com/javase/8/docs/api/java/util/TimeZone.html).
### Does this PR introduce any user-facing change?
No
### How was this patch tested?
By running `./dev/scalastyle`, and manual testing.
Closes#28051 from MaxGekk/doc-time-zone-option.
Authored-by: Maxim Gekk <max.gekk@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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