The relevant issue is only fixed in 23

I was seeing `error: No such remote 'origin'` in the cmake output.
This commit avoids hardcoding `origin` as the upstream URL and instead
uses the `git rev-parse @{u}` to get the configured upstream.

As a follow-up we may want to check if this should be executed by default,
but for now this fixes a warning that I'm seeing with various projects.

And the generated html looks more correct

GIT_SILENT

This fixes spurious differences after a roundtrip through Google Play,
breaking change detection and thus triggering unnecessary metadata
updates.

This considerably simplifies comparing our data with that retrieved from
Google Play for automatically syncing metadata.

Qt maps it this way

This relies on the apparently predominant naming pattern for those files,
those of our apps not using this often do not seem to have an appropriate
file (512x512 png) to begin with.

Explicit override is also possible, by the already existing mechanism of
putting a file with the right name into the fastlane/ source directory.

Having the icon included here will allow it to be automatically synced to
the Play store.

Instead, restore their plain text fallback output that we used to have
already prior to enabling rich text support.