Include whether an email is verified in the /user/emails API endpoint result

Problem to solve

The API result from /user/emails (https://docs.gitlab.com/ee/api/users.html#list-emails) does not indicate whether an email is verified or not. Emails other than the user's primary email can therefore not be used by 3rd-party integrations/apps to validate user identity.

For example, see https://github.com/sourcegraph/sourcegraph/commit/8d13522add2cd1f5da6bee0222c31f15c8ab5cd1

Target audience

3rd-party developer who wants to validate a user's identity against their GitLab identity.

Further details

See above.

Proposal

Just return a boolean indicating whether an email is verified, like the GitHub API does.

What does success look like, and how can we measure that?

Self-evident

Links / references

N/A