Add user setting for toggle typing privacy

[vitormattos]

API side of #9248 to implement an user setting to toggle typing privacy

🏁 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]

• Missing from the list in

  spreed/docs/settings.md

  Line 27 in 70e25dc

  | `read_status_privacy` | `config => chat => read-privacy` | `0` | One of the read-status constants from the [constants list](constants.md#participant-read-status-privacy) |

• Missing in https://github.com/nextcloud/spreed/blob/5ac5d00e2d64f580aadc3257d166c1df4c904313/lib/Controller/SettingsController.php

Please also search if the preference name, capability name or config function is used anywhere else

[SystemKeeper]

Fine by me.
CC: @danxuliu About the capability name, so you're aware