Add basic accessibility features for describing pie chart image detai…

[nickviola]

closes issue 353 and 355. This PR slightly modifies the color scheme in order to reflect the patterns on the charts. This can be changed as needed, but this was what I used in testing that seems to look appropriate.

🗣 Description

This PR adds accessibility aria-labels to the pie charts on the landing page of the dashboard as well as adding patters to the coloring of these pie charts

💭 Motivation and context

To add accessibility features to meet 508 standards.

🧪 Testing

Check the Pie Chart's accessibility with Voiceover or ANDI tool. Also confirm variance in color and patterns.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced
  in code comments.
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.

[ameliav]

Looks like both pie charts are now are text labeled completely and display different patterns along with their different colors.

I found the long description of the pie chart with all the descriptors for the chart here.

@nickviola is there a reason you changed the color scheme though?

[hawkishpolicy]

LGTM.

[ameliav]

LGTM