Use registry secrets for both pulling and pushing

[arttuhuttunen]

Same secret should be used in both pushing and pulling to/from registry, as discussed on Zulipchat https://camel.zulipchat.com/#narrow/stream/257299-camel-k/topic/Pull.20from.20dockerhub.20fails/ .

This is related to problem where after multiple integration builds, integrations can't be built without uninstalling camel k from cluster, as building gets stuck in step where secret isn't used in pulling from private Dockerhub registry and Dockerhub returns error.