Notification Provide Warning Message

# Description

## User Stories

* > As an admin I want that users get informed in all clients with an eye-catching notification so that they can get informed about critical info (ex. outage, deprovisioning grace period etc.).

## Value

## Acceptance Criteria
- new notification type/severity with content "info","error","warning"
- show open notification in web ui, if notification of type/severity "warning" is sent (click on bell closes the message)
- the notification of type/severity "warning" can be dismissed by the user, but will reappear upon next login

## Example: Warning with example for deprovisioning

## Example: Warning with example for outage

## Definition of ready
[ ] everybody needs to understand the value written in the user story
[ ] acceptance criteria has to be defined
[ ] all dependencies of the user story need to be identified
[ ] feature should be seen from an end user perspective
[ ] user story has to be estimated
[ ] story points need to be less then 20

## Definition of done
- Functional requirements
[ ] functionality described in the user story works
[ ] acceptance criteria are fulfilled
- Quality
[ ] code review happened
[ ] CI is green
[ ] critical code received unit tests by the developer
[ ] automated tests passed (if automated tests are not available, this test needs to be created and passed
- Non-functional requirements
[ ] no sonar cloud issues

relates to: https://github.com/owncloud/web/pull/9159/commits/a1f92acdb8131eb2219c07e2b0b2f4973fd12409