Post warning that jetifier is deprecated and won't be called automatically in the future

[mikehardy]

Describe the Feature

I regret not having a link to the discussion but at some point recently we decided AndroidX transition should be done and we should sunset jetifier as an automatic thing.

I've added a deprecation notice to jetifier and now warn any time a file is translated, suggesting the user post a PR to do the AndroidX transition in the repo

https://github.com/mikehardy/jetifier/releases/tag/v1.6.7

Possible Implementations

Just a deprecation notice at first, that jetifier will no longer be automatically called in the future.
Then later, remove the jetifier functionality here.

Related Issues

[mikehardy]

For reference to CLI folks - the deprecation warnings are in jetifier@2