task: add support for excludedMethods

[PieroGr4vy]

Threads excludedMethods through the React Native bridge to both native SDKs.

• Add excludedMethods?: string[] to the Gr4vyConfig TypeScript interface
• iOS: bind in the showPaymentSheet guard, pass through gr4vyInit() to Gr4vy.init()
• Android: add EXTRA_EXCLUDED_METHODS intent extra, extract from ReadableMap, read in Gr4vyActivity and pass to gr4vySDK.launch()

Depends on the companion iOS and Android SDK PRs.