Add histogram graph query handler using go echarts library

[annismckenzie]

What was changed

This adds a new histogram_graph query that returns the HTML with an interactive chart showing the benchmark results.

This is the result if the HTML is saved to a file and opened in a browser (took a screenshot):

Why?

We read the blog post you published at https://mikhail.io/2021/03/maru-load-testing-tool-for-temporal-workflows/ but felt that manually importing the CSV into Google Sheets or something along these lines was too much manual work.

Checklist

1. How was this tested: This is running in our CI pipeline. You basically start a scenario and it's started and monitored while it's running. After the scenario is done, we query the workflow and save the HTML file which can then be viewed directly in GitLab (no manual steps involved at all).

2. Any docs updates needed? I added a section about the new query.

[annismckenzie]

@mikhailshilkov would you want to take a look? This works but isn't fully polished. I wanted to still open the PR to get feedback.