Adding plugin event on shutdown

**Describe the solution you'd like**
Something like **on_shutdown** event allowing plugins to do one last action before going to sleep.
Like backup, handshakes upload, generating last session statistics, clearing the screen...

No file, test, or entry point is named. Start by locating the plugin lifecycle and the code that puts the device to sleep, then determine where a shutdown event could be dispatched. Done means plugins can perform a final action before shutdown, with behavior covered by an appropriate test.

Written by the indexing model from the issue text.