Add the ability to enable service workers on iOS

[gusev-genotek]

PR Checklist

• [ x] The PR title follows our guidelines: https://github.com/Notalib/nativescript-webview-ext/blob/master/CONTRIBUTING.md#commit-messages.
• [ x] There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• [ x] All existing tests are passing.
  • [ x] On Android
  • [ x] On iOS 9
  • [ x] On iOS 10
  • [ x] On iOS 11
  • [ x] On iOS 12+
• [ ] Tests for the changes are included

What is the current behavior?

It is impossible to enable Service Workers on iOS devices

What is the new behavior?

It is now possible to enable Service Workers on iOS devices through the added property of the WebViewExt

Fixes/Implements/Closes #[Issue Number].

[m-abs]

Thank you for the PR. I've merged it and released it with v8.0.2.

Nota is moving away from NativeScript, so the plugin isn't maintained much anymore.