Add entry for License Compliance

Add navigation item to global navigation

• Link to the merge request that introduced the new page: N/A
• Give the MR a descriptive title.
• Optional. Link to the new page: https://docs.gitlab.com/ee/user/compliance/license_compliance/

Note: This page was previously listed in the docs left navigation pane. I don't recall why it was removed, though it may have mistakenly been removed when the feature was deprecated.