List has a11yTitle

[taysea]

Please describe what the rule should do:

Flag if List does not have a11yTitle.

What category of rule is this? (place an "X" next to just one item)

[x] Warns about a potential error (problem)
[ ] Suggests an alternate way of doing something (suggestion)
[ ] Other (please specify:)

Provide 2-3 code examples that this rule will warn about:

<List data={} />

Why should this rule be included in eslint-plugin-grommet?

Best practice accessibility.