Fix(android): Resolve promise for loadWithKeys

[simonljus]

The plugin method loadWithKeys returns a Promise<void> but compared to the other plugin methods, it never resolves.

If a user of a plugin expect the method to resolve, the code will hang indefinitely until some sort of timeout handles it.

Here is also a suggestion for a workaround that would still work after the changes in this PR (the timeoutMs should be tweaked)

let timeoutId: ReturnType<typeof setTimeout>;
const timeout = new Promise((resolve) => (timeoutId = setTimeout(resolve, 5000)));
await Promise.race([
  Intercom.loadWithKeys({ appId, apiKeyAndroid, apiKeyIOS }).finally(() => clearTimeout(timeoutId)),
  timeout,
]);