Android: Move off Java 8 onto the latest release that Github supports

**What is the current behaviour and why should it be changed?**

The Jamulus for Android build process currently requires Java 8 to run. As Java 8 is out of support (since [March 2022](https://www.oracle.com/java/technologies/java-se-support-roadmap.html)), the build should move onto the current GA LTS version (Java 17).

Unfortunately, whilst Android SDK has moved forwards, as of [March 2020](https://www.mobileit.cz/Blog/Pages/android-java-release-train.aspx) only JDK 11 was supported (released 2018). JDK 17 (September 2021) is not yet supported.

**Describe possible approaches**

* Stick with Java 8 until JDK 17 support arrives
* Move to JDK 11 to remain on a supported Java version

I'd suggest we move to JDK 11. It's likely to take some time for Google to move to 17 - there does not appear to be any roadmap published. They may choose to wait until the next LTS after 17 comes out to move onto 17, for example, which will be around 2024.

Note that this does not affect Jamulus itself, only the Android APK packaging.

Arose [here](https://github.com/jamulussoftware/jamulus/pull/2764#issuecomment-1200263790), agreed by @ann0see [here](https://github.com/jamulussoftware/jamulus/pull/2764#pullrequestreview-1056468692) and @hoffie [here](https://github.com/jamulussoftware/jamulus/pull/2764#issuecomment-1201098859).

Start by locating the Android build process and APK packaging configuration, then check where Java 8 is required and which JDK versions the Android SDK supports. Move the packaging build to JDK 11 and verify that the Android APK still builds successfully.

Written by the indexing model from the issue text.