Update 1_connecting.md

Add `spark.cassandra.connection.keep_alive_ms` to list of options that can be set for use by spark-shell.

Should these also be included here as well?

`spark.cassandra.output.batch.size.rows`: number of rows per single batch; default is 'auto' which means the connector will adjust the number of rows based on the amount of data in each row
`spark.cassandra.output.batch.size.bytes`: maximum total size of the batch in bytes; defaults to 64 kB.
`spark.cassandra.output.concurrent.writes`: maximum number of batches executed in parallel by a single Spark task; defaults to 5