refactor: [SIW-1176] Change decoded assertion format on iOS

[LazyAfternoons]

Short description

This PR is a followup to #10 which changes the decoded assertion format to reflect what we expect in our actual backed which requires an authenticatorData and signature as base64 strings. Currently it returns the whole decoded assertion as a base64 string. This change reduces the complexity of the verification downstream.

List of Changes

• Changes the native method decodeAssertion implementation which now returns an object containing authenticatorData and signature as base64 encoded strings;
• Updates the javascript part of the native bridge to reflect the aforementioned change with the proper return type;
• Updates the backend verification function to reflect the aforementioned change;
• Wraps the example app functions in try-catch to prevent unhandled rejected promises in case of error;
• Updates the documentation.

How Has This Been Tested?

• Set value in .env file under example app and backend
• Start metro with cd example && yarn start
• Start backend with cd backend && yarn start
• Using a supported iOS device open Xcode and start the example app
• Try sequentially every button
• Last CTA Verify Assertion should return a value like this {result: {signCount: 1}}

[hevelius]

it should be setAttestation

[LazyAfternoons]

Nice catch, thank you! Fixed in e554377