Add identity verification docs to nav

Add navigation item to global navigation

• Link to the merge request that introduced the new page: gitlab!121592 (merged)

• Give the MR a descriptive title.

• Optional. Link to the review app showing the new page:

• https://pw-add-identity-verification-to-nav.docs.gitlab-review.app/ee/development/identity_verification.html

• https://pw-add-identity-verification-to-nav.docs.gitlab-review.app/ee/security/identity_verification.html