Add encoder for array tag sets

[okapusta]

Use custom params encoder for queries containing tags to allow array as tag value to get multiple metrics in one call. From api docs:

Tags can be searched by AND, OR, and NOT conditions on their tag values. Specifying the same tag name multiple times with different values is an OR.

Example tag set:

query = { 
     resolution: 60, 
     duration: 86400,
     tags: {
       hostname: ['app1', 'app2'],
     }   
}

With NestedParamsEncoder url generated:

https://api.appoptics.com/v1/measurements/psm.plugin.swappiness.page_faults?duration=86400&resolution=60&tags[hostname][]=app1&tags[hostname][]=app2

is invalid and returns 500 error

With ParamsEncoder:

https://api.appoptics.com/v1/measurements/psm.plugin.swappiness.page_faults?resolution=60&duration=86400&tags[hostname]=app1&tags[hostname]=app2

which works.