Migrate from okhttp to ktor for Kotlin

[ben-burwood]

Picking this up from #518 as this feature is of interest.

Motivation for this is that moving to ktor would remove one of the major barriers (the other being MapLibre) to getting this SDK working within a Kotlin Multiplatform Project.

Side note - should probably also consider moving from moshi to kotlinx-seralization in future (or part of this) work as it's Kotlin native, supports KMP out of the box and moshi is now becoming fairly un-worked-on.

The Android Core in this project has a fairly light touch (prtetty much a single call) with okhttp as is so this change should not be significant.
Personally think it is probably worth the breaking change for this dependency but we could abstract a more general httpClient Interface (to use Ktor or Okhttp) if desirable?
Cross compat with okhttp and ktor in the same project is not a concern - other than needing additional dependencies...

When I have some time happy to get started on this in a PR