Add monochrome drawable for android app

With more and more devices getting Android 13, I thought it might be nice if moodle also supported themed app icons.

In order for these to work, a monochrome drawable needs to be supplied.

I only know how to do this for 'vanilla' Android apps, and am not sure how this would be done in the case of Moodle, since I'm not familiar with the technology behind it.

In 'normal' android apps, the steps are as followed:

• add a `ic_laucher_monochrome.xml` drawable to `app/src/main/res/drawable/` (in most cases just a plain white version of the original icon)
• reference this in both the `ic_laucher.xml` and `ic_launcher_round.xml` (latter one optional) that are set in the `AndroidManifest.xml` (most of the time in `app/src/minimap-anydpi-v26/`) using `<monochrome android:drawable="@drawable/ic_launcher_monochrome/>`

I hope this helps if anyone tries implementing this.

I would also be willing to help, but as I already said, someone would have to point me towards some resources about how moodlemobile is built.