[apps] add default route overrides

[aacebo]

• add default route overrides so default routes registered by the app can be overridden by the user
• add tests for router
• add more options to SignInOptions to make it easier to use Unclear usage of overrideSignInActivity #316

bug: #319

[yuqizhou77]

I think with overrideSignInActivity, the SDK will still call token service like const resource = await this.api.bots.signIn.getResource({ state }); and this.api.users.token.get, which will fail if user choose not to use the bot service and OAuth connection for auth.

[aacebo]

I think with overrideSignInActivity, the SDK will still call token service like const resource = await this.api.bots.signIn.getResource({ state }); and this.api.users.token.get, which will fail if user choose not to use the bot service and OAuth connection for auth.

that is correct, our signin method uses our sign in flow, if the developer wants to override the exchange or verify state activities and do their own oauth they can, but they would not use our signin method in that case.