Modify authorization UX to not use system notifications

Currently, when an app must be authorized to connect to a holochain app:
- A modal is displayed over the app, which tells the user to approve via the system notification
- A system notification is generated, which includes an "approve" and "deny" button

This was implemented to fulfill the request by volla that the approval request take the form of a system notification.

After seeing this UX, Volla requested some changes. We may want to take a bit more time designing them to make sure they provide a good UX, similar to familiar apps, i.e. google authentication.

AC:
- Instead of the "approve" and "deny" buttons being in a notification, they are instead:
- Included in the modal overlay
- The overlay includes a button to open the management app to an "Authorizations" page
- The "Authorizations" page contains the "approve" and "deny" buttons
- Consider refactoring so that the modal overlay is created by the `android-service-runtime` app, rather than the client app, by using the "overlay permission" (see https://developer.android.com/reference/android/provider/Settings#ACTION_MANAGE_OVERLAY_PERMISSION)