Add a Cassandra clustering key for data extraction

Add a Cassandra clustering key for data extraction

- Add a partition key
- Use Cassandra key settings to enable data sorting and facilitate proper time-series model training
- Add _Id to the clustering key
- Unify the key column name
- Add lit for test_cassandrasink.py

Issue-ID: AIMLFW-148

Change-Id: Ia624d331fc625e126075a3766132bfc07bf1297a
Signed-off-by: Sungjin Lee <sodyn99@gmail.com>