Add option to clear DB and set DB storage length

[yubiuser]

Close to be a duplicate of

Request: Statistic reset

Please follow the below template, it will help us to help you! Please ensure that you are running the latest version of the beta code. Run pihole -up to update to the latest, then verify that the problem still exists before reporting it. Problem with Beta 5.0: Debug Token: Is it possible to add a (safe) function to reset the ftl-statistics? While searching for it I only found a solution by deleting the old database. An example where this is usefull: Getting a exact view on the summary after …