Update SparkSubmitOperator doc: rename spark_conn_id to conn_id

[enchant3dmango]

There is no spark_conn_id in the SparkSubmitOperator, there is a conn_id for the Spark connection.

Screenshot:

[boring-cyborg]

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[phanikumv]

nice catch 👍

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.