build:android - allow for passing custom gradle args

[x] I've read the Contribution Guidelines.
[x] I've updated the CHANGELOG if necessary.
[ ] I've ensured the unit and smoke tests are still passing - either by running yarn test:unit and yarn test:smoke:[ios|android] or by checking the appropriate CircleCI builds' statuses.
[x] I've manually tested whether the changes I made work as expected.

I added a new build:android option: --gradle-args. It can be used to pass custom arguments to gradle, like --stacktrace.

expo / turtle