feature request: Notifications actions

**Is your feature request related to a problem? Please describe.**
I miss the possibility to react directly from some notifications, from the notification itself, without the need to open the main gotify interface.

**Describe the solution you'd like**
I would be able to pass some "extras" parameters that add some actions directly in the notifcations, like copy a text, open a link, or share a text/link, even why not call/text a contact.

**Describe alternatives you've considered**
I tried a simple implementation of "share" and "open" a link here, its working but can be done better maybe, please take time to read this PR thread: https://github.com/gotify/android/pull/236 .

**Additional context**
Please see this link https://github.com/gotify/android/pull/236 where you can find an example of integration with hauk-snitch project for
example.
Another common example is the integration of gotify with a monitoring, on-call setup. You can receive some events/alert and want to add some actions, open a link, ack an alert, escalade to another guy through call or text, copy a code you receive to the clipboard.