Stateless cooldown system

[lemonsaurus]

Currently, we're creating a json file to store cooldown information, implemented in #83. This works very well for local setups, but it's not a good option for Kubernetes CronJobs because it requires persistence, and generally Blackbox will not be used that way. It will be destroyed after every run.

So how can we solve this without requiring persistent data to be stored locally? It's simple - we just store the json file in the storage that the user has configured, and fetch it again from the storage when we're starting up. I mean, everyone has storage, otherwise Blackbox doesn't work, so we can rely on that being available no matter what.

[lemonsaurus]

Might be nice some day, but not important.