Mango query explain page

[mharrigan26]

Overview

This PR adds a parsed view of the Explain Page to accompany the addition of index_candidates to the /_explain endpoint in Couch 3.4. The current page is very bare bones and provides no guidance to users in terms of why a index was selected or not. The parsed page would indicate the selected index along with other possible candidates and why they were not selected. This is to help the user better understand and make more efficient queries.

Testing recommendations

Run a mango query on a database. Select Explain and check that there is now a parsed output and raw json output explaining the query.

GitHub issue number

Related Pull Requests

Checklist

• Code is written and works correctly;
• Changes are covered by tests;
• Documentation reflects the changes;
• Update rebar.config.script with the correct tag once a new Fauxton release is made

[Antonio-Maranhao]

+1 provided all checks pass