Fix: process percentile metric queries to display values on the frontend

[kevinwcyu]

What this PR does / why we need it:

• Fixes an issue where percentile metric query types were not being processed. processAggregationDocs did not have a case for the percentilesType type so it was not processing it correctly.
• Fixes an issue where extended stats metric query types only returned 1 value, if multiple were specified in the query (e.g. if you selected min and max, it would only return max. The break statement caused the processing to only process the first extended stat metric.
• Fixes an issue where the extended stats label only returned Extended Stats instead of Extended Stats {stat name} e.g. if min was one of the selected stats it should say Extended Stats Min in the label.

Which issue(s) this PR fixes:

Fixes #587

Special notes for your reviewer:

You can test this by:

1. Build the data source
2. yarn server
3. Add sample data
4. Run the queries below using the default provisioned data source

Query

Result

Explore

[idastambuk]

👏🏻