QAN App Get Filters API end point Response time could be improved

User Impact: Bad QAN performance when applying filters or interacting with QAN app gives a feeling to not use this tool anymore.

PMM-QA set up another long-running instance with a good amount of queries executing on all 3 major databases. 

2 Core, 4 GB RAM PMM-Server Host

The idea behind this was to observe the load timing for several components in the QAN app. 

1) QAN overview, this seems to be loading in fair time when we have about 25k distinct queries it takes roughly 13 seconds to load the data, of course, there is the scope of improvement here, but we need to set this based on some parameters and metrics defined by PM and Engineering. [/v0/qan/GetReport]

2) What's not really obvious and acceptable is the amount of time Filters take to load, the moment you keep increasing the time range from last 12 hours default to last 7 days and then finally to last 30 days. 

The load timing of QAN filters section, /v0/qan/Filters/Get keeps increasing for the same load with which the overview 

Fetching response for last 7 days takes around 33 seconds, fetching last 30 days takes around 40 seconds to load just the filter section.