Version in APM status does not get populated (no reconciliation)

[sebgl]

I was playing with E2E tests to cover strict version upgrades, and noticed in some cases the APM status.version field never gets populated, because no reconciliation happened.

I think this is simply because we did not catch the version change in the last updated Pod (no reconciliation triggered).

2 options to fix this:

1. watch APMServer Pods, to reconcile on any change
2. compute the version status field based on the deployment resource (instead of checking that all Pods run 7.8.0, check that the deployment resource specifies 7.8.0, that generation matches observedGeneration, and that all replicas are ready... it's a bit trickier)

I think 1) is simpler to implement, and we already watch all Pods as part of the ES controller anyway.

I suspect it is also required for any controller that manipulates Pod-level information. Which is true, besides status.version, for:

• changing the deployment strategy for Kibana version upgrades
• calling the read-only endpoint for Enterprise Search version upgrade