Add advertisingSid property to ScanResult and RxBleInternalScanResult

[KrzysztofMamak]

Is your feature request related to a problem? Please describe.
com.polidea.rxandroidble2.scan.ScanResult does not contain an information about advertising sid which is needed for supporting Bluetooth Auracast feature (https://www.bluetooth.com/wp-content/uploads/Files/Specification/HTML/24670-BASS-html5/out/en/index-en.html#UUID-2a17a3a2-36f9-8cb4-0877-3b56055a7955). It means that there is no option to retrieve this information from the rxandroidble library.

Describe the solution you'd like
com.polidea.rxandroidble2.scan.ScanResult and com.polidea.rxandroidble2.internal.scan.RxBleInternalScanResult classes can be extended with advertisingSid property. This value can be retrieved using android.bluetooth.le.ScanResult.getAdvertisingSid method (https://developer.android.com/reference/kotlin/android/bluetooth/le/ScanResult#getadvertisingsid) and propagated in com.polidea.rxandroidble2.internal.scan.InternalScanResultCreator.

I can volunteer and submit a PR soon.

[dariuszseweryn]

Hey, sorry for a long pause, got a busy time at work. Feel free to open a PR 👍

[KrzysztofMamak]

I'll open a PR soon.

[dariuszseweryn]

I have one request, when adding tests please use JUnit – I've started migrating to it from Spock as it's not supported for Android anymore.