The new subcommands operate on a single APPID:VERSIONCODE pair, so this new
function fetches the metadata needed for that operation, and includes any
required checks.
The algorithm came from:
uniqx/fdroidserver@2b779e6599
This reworking of it includes:
* removed `check_disabled`, seems like the scheduler should handle that? If
it is required, it can be added later.
* standard variable names
* fixed spelling errors and hopefully improved docstrings
* black format
* added tests
* standardized the strings, made them localizable
b00b9c9390
