[A11y] e2e baseline tests for a11y screen reader descriptions

[markov00]

We should add e2e accessibility tests to assert screen reader summaries for different chart types and configurations.
The aim is to get a baseline of the current state of these summaries before we merge the improvements being worked on in #2683. This will allow us to track regressions/improvements in a better way.

[markov00]

close by #2684