VM Dashboard polishing

Improve VM dashboard :

• Element: "Time before run out of space"
  It's required to increase used period in the formula. Period 1h does not make sense as chunks are volatile for short periods of time.
  
• Element: "Index Size"
  Spark lines has to be limited by Y-min = 0 value.
  
• Element: "Active Time Series Changes"
  The used metric is gauge so the formula has to be rewritten.
  
• It's required to add an element that would show amount of Scrapped Targets
  (VM has metric vm_promscrape_targets)
  As we’re looking to move to “push” reporting both push/pull targets may be interesting.
• Row names has to be corresponding to shown elements
  e.g.
  General requests, Queries Duration are reported in the Scraping row
  
• Element: "Queries Duration Details"
  Queries duration is shown on another element so it's better to replace this chart by another one "Amount of Queries".
  
• Element: "Time Series"
  Row: "Troubleshooting"
  The chart is overloaded. It's required an investigation in order to replace this element by some less complicated charts.