So far generic describe (`DESC <name>`) followed Cassandra implementation and it only described keyspace/table/view/index.
This commit adds UDT/UDF/UDA to generic describe.
Fixes: #14170Closesscylladb/scylladb#14334
* github.com:scylladb/scylladb:
docs:cql: add information about generic describe
cql-pytest:test_describe: add test for generic UDT/UDF/UDA desc
cql3:statements:describe_statement: include UDT/UDF/UDA in generic describe