build(nix): add outputs for Android binaries

[link2xt]

This change will result in automatic publishing Android binaries for deltachat-rpc-server when GitHub release is published. Normal musl-based Linux binaries are difficult to use on Android because they expect /etc/resolv.conf to contain nameserver addresses, while on Android this file is not present and DNS works via UNIX socket proxy that only bionic libc uses.

Using NDK 24 because NDK 23 does not have getauxval() function. In Delta Chat Android we use NDK 23, but this requires building our own fake getauxval().

No wheels yet and they are not planned for this PR because we cannot upload them to PyPI anyway.
For wheels we can use https://peps.python.org/pep-0738/ as a standard for wheel tags, e.g. android_21_arm64_v8a, android_21_x86_64, android_16_x86, android_16_armeabi_v7a.
If we build such wheels, we need to publish them to some other registry. GitHub Packages does not support Python yet.

[link2xt]

This is ready for review.
Testing by manually triggering workflow with gh workflow run deltachat-rpc-server.yml --ref link2xt/deltachat-rpc-server-android. This builds all the binaries but does not upload them because there is no release.
Runs can be seen at https://github.com/deltachat/deltachat-core-rust/actions/workflows/deltachat-rpc-server.yml