Undocumented supported apps

Some supported apps lack documentation of any sort in the Admin Manual.

• Circles
• Collaborative tags
• First Run Wizard
• Full text search
• Group folders
• Guests
• Monitoring
• Announcements
• Notifications
• Photos
• Recommendations
• Related resources
• SharePoint Backend
• Suspicious Login
• SSO & SAML authentication
• Social sharing
• Terms of service
• Two-Factor backup codes
• Two-Factor WebAuthn (replaces U2F)
• Talk
• ONLYOFFICE
• Global Site Selector
• Mail

The above should probably each have at a minimum:

• a brief page/section under Configuration (or elsewhere if more appropriate)
• a section in the occ commands chapter (where applicable)

The following don't have much (if any) in the way of admin facing settings/commands, but a brief paragraph mentioning them in the Admin Manual seems appropriate (since they're supported and/or shipped apps). At a minimum describing "What this app does":

• Deck
• Comments
• Contacts Interaction - https://github.com/nextcloud/server/pull/19075
• Data Request
• Nextcloud Announcements
• PDF Viewer
• Share by Mail
• Calendar (distinct from CalDAV)
• Contacts (distinct from CardDAV)
• Lookup Server Connector

TODO:

• Create dedicated issues for each of the above apps and edit this issue with links to them

Start by reviewing the Admin Manual's Configuration and occ commands chapters, then compare the listed supported apps with existing coverage. Split the work into dedicated issues as requested, documenting each app's purpose and, where applicable, its settings and occ commands. Done means the apps have appropriate Admin Manual coverage and this issue links the follow-up issues.