feat: scrape selected jobs via query params

[burningalchemist]

resolves #178

We can call the endpoint with the query parameter jobs[] to scrape only selected jobs:

localhost:9399/metrics?jobs[]=dbtargets1&jobs[]=dbtargets2

In Prometheus configuration we can use this syntax under the scrape config:

  ...
  params:
    jobs[]:
      - dbtargets1
      - dbtargets2
  ...