Describe the feature you'd like to request

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 an audio file file to md.

To do so:

• add info to capability like https://github.com/tobiasKaminsky/declarativetest/blob/main/lib/Capabilities.php#L29
• create an endpoint that can receive a fileID and create a MD file out of it

Ref: #312

Describe the solution you'd like

See above

Describe alternatives you've considered

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