Previously, scrapers would scrape the target 10 times. This was
because each scraper subscriber was not put into a queue group.
I've added the queue group "metrics" and now we the subcribers
will only scrape the target once.
Additionally, I moved to using nats memory instead of nats file
store. We don't need durability for scraper runs across restarts.
Kelvin Wang
Ben Johnson
Michael Desa
Chris Goller