Misc changes (see MR description).

This MR:

• adds an error check to unmarschalling of JSON file with images list. This file is an internal implementation detail, hence crude panic instead of gracefull error message
• fixes issue with publishing errortracking/tracing images discussed here.
• fixes #1697 (closed) - moves readiness checks to Gin framework
• update docker tags references while we wait for #1759 (closed) to be addressed

#1697 (closed) was asking for moving heath checks to Gin, but after giving it some thought I think a better approach is to move only the readiness checks instead. Gin is wired with Redis as middleware, in case when Redis fails, pod gets restarted which very likely will not fix the issue with Redis. Readiness check however only removes given pod from k8s load balancer without restarting the pod. Once Redis is back, pod is re-added.