[Accessibility] Improve Roles Accessibility

[elasticmachine]

Original comment by @aphelionz:

1. Permissions Radio buttons are not properly marked up with labels, number of choices.
2. The tag inputs here are not usable by keyboard
3. When creating / deleting new fields using these controls, consider auto-focusing on the created field, or a relevant field or nearby button after deletion

[cjcenizal]

This is still valid as of 6.4.

[AlonaNadler]

Thanks for updating @cjcenizal

[elasticmachine]

Pinging @elastic/kibana-security

[legrego]

Since the role management screen was redesigned for 6.5, we will need to reevaluate this to see how accessible the new design is.

[rayafratkina]

Looks like at least some issues remain after redesign, so assigning a level label

[myasonik]

Everything seems to be working as expected now