'ndk_paths' will be automatically filled out from well known sources
like $ANDROID_HOME/ndk-bundle and $ANDROID_HOME/ndk/*.  If a required
version is missing in the buildserver VM, it will be automatically
downloaded and installed into the standard $ANDROID_HOME/ndk/
directory.  Manually setting it here will override the auto-detected
values.  The keys can either be the "release" (e.g. r21e) or the
"revision" (e.g. 21.4.7075529).

https://developer.android.com/studio/projects/configure-agp-ndk#agp_version_41
* sdkmanager installs "ndk;12.3.4567890" into $ANDROID_SDK_ROOT/ndk/
* sdkmanager installs "ndk-bundle" into $ANDROID_SDK_ROOT/ndk-bundle/