Feature/revert subscription status

Changes in this pull request

Reverts subscription status back to being an enum.

[x] All tests pass. Demo project builds and runs.
[ ] I added tests, an experiment, or detailed why my change isn't tested.
[x] I added an entry to the CHANGELOG.md for any breaking changes, enhancements, or bug fixes.
[x] I have run swiftlint in the main directory and fixed any issues.
[ ] I have updated the SDK documentation as well as the online docs.
[ ] I have reviewed the contributing guide