REST Service missing sessionAffinity causes job run failure with HA cluster

When using a Session Cluster with multiple Job Managers, the -rest service load balances the API requests to all job managers, not just the master.

When submitting a FlinkSessionJob, I often see errors like: `jar <jar_id>.jar was not found`, because the submission is done in 2 steps: 

• upload the jar with `v1/jars/upload` which returns the `jar_id`
• run the job with `v1/jars/<jar_id>/run`

Unfortunately, with the Service load balacing between nodes, it is often the case that the jar is uploaded on a JM, and the run request happens on another, where the jar doesn't exist.

A simple fix is to append the `sessionAffinity: ClientIP` on the -rest service, where the API calls from a given originating IP will always be routed to the same node.

This issue is especially problematic with Beam, where the Beam job submission does not retry to run the job with the jar_id, and will fail, causing it to re-upload a new jar and retrying, until it is lucky enough to get the 2 calls in a row routed to the same node.