* [MM-57066] Add metric counters for notification events
* Some small changes
* Account for Metrics() sometimes being nil
* Fix test (again)
* Fix more tests
* A few changes from testing - added success counter
* Missed a mock
* Lint
* Add feature flag for notification monitoring
It was a good decision in hindsight to keep the public module as 0.x
because this would have been a breaking change again.
https://mattermost.atlassian.net/browse/MM-53032
```release-note
Changed the Go module path from github.com/mattermost/mattermost-server/server/v8 to github.com/mattermost/mattermost/server/v8.
For the public facing module, it's path is also changed from github.com/mattermost/mattermost-server/server/public to github.com/mattermost/mattermost/server/public
```
https://mattermost.atlassian.net/browse/MM-52079
```release-note
We upgrade the module version to 8.0. The new module path is github.com/mattermost-server/server/v8.
```
Co-authored-by: Doug Lauder <wiggin77@warpmail.net>
