Adds paywall decline - Githubissues

Changes in this pull request

A user can add paywall_decline as a trigger to present a new paywall after dismissing a paywall.

[ ] All tests pass. Demo project builds and runs.
[ ] I added tests, an experiment, or detailed why my change isn't tested.
[ ] I added an entry to the CHANGELOG.md for any breaking changes, enhancements, or bug fixes.
[ ] 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