Add functionality to look-up and display chart on embeddable Insights page

Add functionality to look-up and display chart on embeddable Insights page

• This page should display one chart based on index
  • Get chart from the insight.json page definition (examples here: /groups/gitlab-org/-/insights.json, /gitlab-org/gitlab/insights.json, and fixture here: https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/fixtures/insights/default.yml)
  • Needs to grab the group/project and the category/path="insights" from the URL. Update: Just do the same as the insight page is already doing to create the query and then read the chart index from the URL param.
  • An example of a request to this page could look like this: https://gitlab.com/gitlab-org/gitlab/insights/embedded?index=0
  • The index is used to look up the chart in the insights.json above
  • If there is no index param, return an error message
  • If the chart is not found it should return an error message