Documentation: determining whether something is a high risk accessibility concern

[dav-idc]

What

Add a flowchart-type set of documentation on the process of determining a

Why

• helps expand on the prioritisation info on the accessibility strategy
• allows more team members beyond the accessibility specialist to carry out an assessment of accessibility risk
• standardises our format for recording accessibility risk in GitHub issues

This is related to a broader epic about adding accessibility documentation to our playbook:

• Add accessibility documentation to Design System Team Docs website govuk-design-system#3077

Who's doing work on this

Accessibility specialist

Who should review

Developers, other team members

### Tasks
- [ ] Gather examples of existing assessments
- [ ] Create a template for assessments
- [ ] Write instruction steps for making the assessment
- [ ] Create a flowchart for when to do this risk assessment and when it's not so necessary
- [ ] Write intro and background info, linking to accessibility strategy
- [ ] Send for review by the team

[dav-idc]

This will not be completed by me before I leave GDS 😢

I recommend handing this to the next accessibility specialist.

FYI @kellylee-gds @stevenjmesser