Add lcpserver endpoint to get content info from licence id

[Thomashrb]

Add a way to given the license id lookup content info.
We already have all of the information we need available in the lcpserver database.

This mr puts the endpoint at licenses/{license_id}/content which then returns the index.Content domain object.
From the outside this looks like:

curl "<lcpserver base url>/licenses/<license id>/content" | jq
{
  "id": "<some content id>",
  "key": "<some content key>",
  "location": "<some content location>",
  "length": <some content length>,
  "sha256": "<some content sha>",
  "type": "<some content type>"
}