Add endpoint that generates ISCCs from URLs #49

An endpoint that accepts a media asset URL and embeddable metadata as input.
The service should download the asset, embed metadata (if any), generate an ISCC asynchronously while blocking the client until the response is ready. The URL of the modified local media asset will be in the response so it is available for download within the cleanup timeout.

Open Questions:

Should the download be locked to the IP that created the request or should it be open for download.

If the processing result and/or modified asset needs to be stored somewhere else it might make sense to allow to provide a callback URL with the request, such that the server can push the result(s) to the provided callback URL.

If there is a callback URL the server wouldn´t need to block the client. Instead the server could return a job-id instantly. If the client needs to know the job status it could query the server.