Is your feature request related to a problem? Please describe.

Let clients create new contacts.

Describe the solution you'd like

Related to nextcloud/files-clients#86 (comment)

With Declarative UI any server app can add interactions dynamically to Files clients.
This reduces code on client side and gives lots of opportunities to display simple stuff in a native way or interact in an easy way.

To have a starting set, we discussed and defined some actions.
One action is to offer an menu entry in context menu to convert a docx file to md.
(We can add later more).

To do so:

• add info to capability like https://github.com/tobiasKaminsky/declarativetest/blob/main/lib/Capabilities.php#L29
• create an endpoint that renders via protocol a form with all relevante info
  • Example for a form is: https://github.com/tobiasKaminsky/declarativetest/blob/main/lib/Controller/ApiController.php#L84
• create an endpoint to receive the info and create a vCard via \OCP\Contacts\IManager::createOrUpdate

Describe alternatives you've considered

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Additional context

No response