[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)