install apksigner on releases that have it, and require jarsigner

apksigner is basically a requirement for modern fdroidserver versions. android-sdk is already included, that means the OpenJDK is, so this should only add apksigner packages to the install. jarsigner is needed to sign and verify index files. android-sdk only Recommends: it, so it needs to be required here.

(FYI this ansible task will be used in the CalyxOS repo server)