Download CSV from Prometheus charts on the metrics dashboard

Problem to solve

In order to ensure that charts are accessible to screen-readers, we should allow for the downloading of CSV data from the chart so it can be fed into an application that will more accessible.

Intended users

Users interacting with GitLab via screen-readers.

Further details

Design

This issue will add in Download csv option into the dropdown menu that we will create separately as part of https://gitlab.com/gitlab-org/gitlab-ce/issues/63197:

The first implementation of this issue with be fron-end only, respecting the limit of ~600 data points that allows us to load this with the chart and not fetch more data.

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

Links / references