[ISSUE #570] ASoC runtime optimization: Cassandra connectors

[imaffe]

What is the purpose of the change

1. implement Cassandra source/sink connectors

Brief changelog

1. added Cassandra sink and source connector implementations

Verifying this change

XXXX

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[imaffe]

1. the rat check failed because of a requirment.txt, but I looked at other Apache python projects (like airflow), it seems one file like this without license declaration is ok

[RongtongJin]

There are some useless comments, it is better to delete them.