feat: Allow guests to contacts user via public profile "Talk to" link

[jonas2515]

☑️ Resolves

• Fix Website integration/click-to-call #674

Depends on nextcloud/server#40288

🚧 Tasks

• Conversation name should be in recipient language
• Admin config to disable globally/per-user? (will be done in another PR)
• Check that API endpoint respects the users profile setting (right now only the button is hidden) feat(profile): Add public interface for profile manager so apps can check config server#41055
• Make sure the actual conversation is only created on a subsequent POST request. Otherwise like preview generation etc. will randomly create new conversations.

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not required
• 📘 API documentation in docs/ has been updated or is not required
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required
• 🔖 Capability is added or not needed

[nickvergessen]

I can afterwards take care of the rebase and adding the admin config as discussed.

[nickvergessen]

Ah, this is still open:

• Make sure the actual conversation is only created on a subsequent POST request. Otherwise like preview generation etc. will randomly create new conversations.

[nickvergessen]

Need to check if @DorraJaouad has time at the end of the cycle to work on this