Inform user when assigned resource change state

### What feature do you want to see added?

As user who reserve a resource I want be inform when the status changes:
+ other person unreserve my resource
+ resource is reassign to other user
+ resource shall be locked (via job). This is helpful, when user locks resource for very long time and other jobs are blocked.

This might works only for users with valid email.
It shall be also implemented a extension point here, to allow other plugins contribute here (Teams notification, Slack ...)

### Upstream changes

_No response_