* Add interface for PreferencesHaveChanged hook
* Add context to preference-related methods of App
* Implement PreferencesHaveChanged
* Re-add missing "fmt" import
* Update minimum server version for the new hook
* Remove pointers to be consistent with other preference APIs
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
```
