Domain Picker: add jest-axe for a11y testing

[ciampo]

What

Use axe (an a11y testing tool) in the Domain Picker automated tests by using the jest-axe integration

Why

This will help spotting the most obvious a11y issues in our code just by adding one additional insertion in any tests.

A/C

• [ ] Add jest-axe to Calypso's dev dependencies
• [ ] Add jest-axe to the Domain Picker package's jest configuration
• [ ] Add Axe configuration options (e.g. what type of a11y issues should be flagged)
• [ ] Add axe expectation/assertions in current tests
  • [ ] As axe assertion fails, we should open separate issue for every failure

Context

Later on, when adding Storybook to the package, we should consider adding the a11y plugin and sharing the same Axe configuration with the jest-axe plugin

[youbrokesomething]

The jest-axe package and the axe-playwright packages are going to be added as part of my improving accessibility on Dotcom projcet.