Support for registering to connection events

[mikolak]

iOS 13 has introduced new API that allows one to register for connection events. https://developer.apple.com/documentation/corebluetooth/cbcentralmanager/3174844-registerforconnectionevents

I've received a PR in MBA introducing it: https://github.com/Polidea/MultiPlatformBleAdapter/pull/56/files
Since I'd like to get rid of forked RxBluetoothKit inside Multiplatform BLE Adapter and switch Cocoapods version, it'd be nice to not have to patch it myself later. ;)