Add processing of embedded share

[rawe0]

This PR adds the processing endpoint for an embedded share

• For now this only changes the state to accepted (or pending if you want to "unprocess" the share).
• Eventually we want the downloaded content to arrive in the target folder, the target is just logged for now.

Has been tested using curl.

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.