Kw/update rn sentry cli commands

[krystofwoldrich]

Closes: #181

Relates to CLI update in RN SDK getsentry/sentry-react-native#2246 and getsentry/sentry-react-native#2457

[krystofwoldrich]

The sentry.properties file in ios dir would like like this:

debug_files.upload.include_sources=true

[krystofwoldrich]

I've simplified this to env SENTRY_INCLUDE_NATIVE_SOURCES. This way it should be simple enough to opt-in for the feature and it won't affect the cli properties file.

[marandaneto]

We can specify this on the docs as well https://docs.sentry.io/platforms/react-native/upload-debug/
How to export the var or add it manually via the UI on Xcode.