* (WIP) Refactor the ImageStore interface to work with our latest alerting repository
* update alerting package
* refactor, new URLExists method in ImageProvider
* tests for the new methods
* fix linter warnings
* use alertingImages as an alias for grafana/alerting/images
* logs about image uris and not found images
* nerf image not found logs
* extract duplicated code to getImageFromURI() method
* refactor getImageFromURI()
* add index on url
* add comment about migration log
* sync generated files