[SPARK-40574][DOCS] Enhance DROP TABLE documentation
[SPARK-40574][DOCS] Enhance DROP TABLE documentation

### What changes were proposed in this pull request?

This PR adds `PURGE` in `DROP TABLE` documentation.

Related documentation and code:
1. Hive `DROP TABLE` documentation:
    https://cwiki.apache.org/confluence/display/hive/languagemanual+ddl
    <img width="877" alt="image" src="https://user-images.githubusercontent.com/5399861/192425153-63ac5373-dd34-48b3-864c-324cf5ba5db9.png">
2. Hive code:
    https://github.com/apache/hive/blob/rel/release-2.3.9/ql/src/java/org/apache/hadoop/hive/ql/metadata/Hive.java#L1185-L1209
3. Spark code:
    https://github.com/apache/spark/blob/v3.3.0/sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveShim.scala#L1317-L1327

### Why are the changes needed?

Enhance documentation.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

manual test.

Closes #38011 from wangyum/SPARK-40574.

Authored-by: Yuming Wang <a045e9e381e8d6ed98f3af6ea924f96c8dd7fbad@ebay.com>
Signed-off-by: Dongjoon Hyun <6ff48b33cbb828151035af58a92f18a39f1d1036@apache.org>

holdenk/spark,witgo/spark,mahak/spark,shaneknapp/spark,holdenk/spark,dongjoon-hyun/spark,vinodkc/spark,HyukjinKwon/spark,mahak/spark,witgo/spark,apache/spark,zzcclp/spark,holdenk/spark,witgo/spark,zzcclp/spark,ueshin/apache-spark,hvanhovell/spark,dongjoon-hyun/spark,hvanhovell/spark,apache/spark,wangyum/spark,witgo/spark,ueshin/apache-spark,ueshin/apache-spark,vinodkc/spark,ueshin/apache-spark,hvanhovell/spark,witgo/spark,srowen/spark,ueshin/apache-spark,srowen/spark,HyukjinKwon/spark,vinodkc/spark,holdenk/spark,mahak/spark,srowen/spark,mahak/spark,srowen/spark,vinodkc/spark,dongjoon-hyun/spark,wangyum/spark,srowen/spark,vinodkc/spark,HyukjinKwon/spark,wangyum/spark,zzcclp/spark,shaneknapp/spark,witgo/spark,zzcclp/spark,shaneknapp/spark,shaneknapp/spark,apache/spark,ueshin/apache-spark,hvanhovell/spark,mahak/spark,hvanhovell/spark,ueshin/apache-spark,wangyum/spark,holdenk/spark,holdenk/spark,vinodkc/spark,holdenk/spark,apache/spark,wangyum/spark,apache/spark,shaneknapp/spark,wangyum/spark,apache/spark,mahak/spark,dongjoon-hyun/spark,shaneknapp/spark,zzcclp/spark,hvanhovell/spark,shaneknapp/spark,HyukjinKwon/spark,srowen/spark,dongjoon-hyun/spark,HyukjinKwon/spark,witgo/spark,apache/spark,HyukjinKwon/spark,wangyum/spark,HyukjinKwon/spark,dongjoon-hyun/spark,dongjoon-hyun/spark,hvanhovell/spark,zzcclp/spark,mahak/spark,zzcclp/spark,srowen/spark,vinodkc/spark