APIv5

This MR combines the required changes in this repository and it's dependencies (bitmask-core-mobile) for a API V5 provider setup.

It also contains the remaining bits to setup a provider via an invite code.

APIv5 endpoints return ed25519 or ecdsa private keys for the VPN setup. The MR completes the support for both.

The MR integrates a swagger Java code generator and tooling to fetch menshen's swagger definition and generate the api client code. The code in app/src/main/java/io/swagger can be skipped during the review, since it's autogenerated.

closes #9202 (closed)