Add default ETL user to OpenSRP deployments

[gstuder-ona]

When the canopy team is asked to integrate OpenSRP with the canopy platform, one of the most time-consuming steps is often just getting credentials for an ETL user for a particular OpenSRP instance. We generally can't use a generic test user, as those users don't have permission for the "getAll" endpoint, so we're forced to find the owner of the OpenSRP instance and do a bunch of back-and-forth to have the owner manually create our user. Often the instance gets redeployed at some point (maybe weeks later), and I suspect the etl-user configuration isn't stored anywhere so it just "disappears" and our ETL flows just stop pulling data at what appears to be a random point in time.

It'd be nice if, out of the box, OpenSRP was setup with a default ETL user so that all that would be required would be the opensrp send a password (and keycloak credentials) for that particular instance. If there's another solution that achieves this or I misunderstand how opensrp credentials are configured that'd be cool to know too.

[gstuder-ona]

@pld just attaching you as this is a cross-team issue - not super high priority, but we've seen credentials disappear enough times that I think it's worth addressing

[pld]

k assigning to @manutarus, this sounds like it'd fit into the k8s work on OpenSRP