[Uptime] Use core HTTP instead of native fetch for API calls

[andrewvc]

We use plain fetch in a number of places, notably all the files in state/api. We should switch these to use core http as in use_telemetry.

For the API calls however this is a bit trickier since useKibana is only available in the component, and breaks when invoked after dispatch from redux. We should introduce some sugar to making these dispatches more simple, so we don't have to put useKibana everywhere.

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)

[justinkambic]

A possible solution is to use a custom hook that provides a function we can wrap our dispatched actions in that will add Kibana's fetch to the action payload, and we modify our API calls to expect a fetch function as a dependency.

This will keep the API functions pure and stateless, and make them more testable since the fetch function is injected now vs. referenced directly from the function body.

That said, this is only one of other potential solutions, and I'm interested to hear other proposals on the best way to resolve this.

[andrewvc]

@shahzad31 would love to hear your thoughts here as well.