allow specify --numeric-version with APK_NUMERIC_VERSION env

[zebra-lucky]

• add default=os.environ.get('APK_NUMERIC_VERSION', None) to --numeric-version argument

[AndreMiras]

Thanks @zebra-lucky for the PR.
The code looks OK, but apart from not having unit tests I have mixed feelings about this feature 🤔
It basically introduces inconsistencies in the way we deal with arguments has it would be the only argument of this file that comes with "hybrid" way of setting it up.
I suppose this is a follow-up from kivy/buildozer#1079, but I'm wondering why didn't we do with a normal buildozer.spec file parameter rather than with environment variable?
I'm not completely against the feature however, just need to think and discuss it further.
I'm wondering what @inclement thinks about it too

[zebra-lucky]

I suppose this is a follow-up from kivy/buildozer#1079, but I'm wondering why didn't we do with a normal buildozer.spec file parameter rather than with environment variable?

For me env approach is more flexible and versionCode can be calculated with use of other build env variables (APP_ANDROID_ARCH=arm64-v8a as example).

Additionally it was simle to add changes)

І'l look how to add unit testing tonight.

[obfusk]

buildozer now supports setting APP_ANDROID_NUMERIC_VERSION.