v0.28.0

We had to rename project.ext.sentry to project.ext.sentryCli because our own proguard gradle plugin was conflicting with the name.
The docs already reflect this change.
#257

We now use the mainThread to report errors to RNSentry. This change is necessary in order for react-native to export constants.
This change shouldn't impact anyone using react-native-sentry since most of the "heavy" load was handled by sentry-cocoa in its own background queue anyway.
#259 #244

Bump sentry-cocoa to 3.8.3