[Monitoring] Replace angular $http with Kibana core http service

[chrisronline]

We recently had to fix a couple of things that look related to the $http service that Angular provides (see #81375 and #81200). Since we do not really need to use it, we should switch to using the core http service provided by the Kibana platform.

[elasticmachine]

Pinging @elastic/stack-monitoring (Team:Monitoring)

[matschaffer]

Closing in favor of angular removal #111309

We're already using kibana http in the react versions of the angular views.