Improve document API responses when modifying document type which is not assigned to any clusters

[jonmv]

The document type system is not assigned to any cluster. This gives the following responses:

➜  app git:(master) ✗ fcurl /document/v1/db/system/docid/7.230.4 -X PUT -d '{ "fields": { "name": {"assign": "main"} } }' | jq .
{
  "errors": [
    {
      "description": "DOCUMENT_EXCEPTION Received unknown response: com.yahoo.documentapi.messagebus.protocol.DocumentIgnoredReply@40136140",
      "id": -11
    }
  ],
  "id": "id:db:system::7.230.4",
  "pathId": "/document/v1/db/system/docid/7.230.4"
}

➜  app git:(master) ✗ fcurl /document/v1/db/system/docid/7.230.4 -d '{ "fields":{ "name": "main" } }'| jq .
{
  "id": "id:db:system::7.230.4",
  "pathId": "/document/v1/db/system/docid/7.230.4"
}

➜  app git:(master) ✗ fcurl /document/v1/db/system/docid/7.230.4 | jq .
{
  "errors": [
    {
      "description": "UNSPECIFIED com.yahoo.documentapi.DocumentAccessException: [UNKNOWN(251012) @ tcp/h22822a.prod.aws-us-east-1a.vespa.aws.oath.cloud:19109/default]: Unknown bucket space mapping for document type 'system' in id: 'id:db:system::7.230.4' \n\tat com.yahoo.documentapi.messagebus.MessageBusSyncSession.get(MessageBusSyncSession.java:148)\n\tat com.yahoo.documentapi.messagebus.MessageBusSyncSession.get(MessageBusSyncSession.java:133)\n\tat com.yahoo.document.restapi.OperationHandlerImpl.get(OperationHandlerImpl.java:292)\n\tat com.yahoo.document.restapi.resource.RestApi.handleGet(RestApi.java:266)\n\tat com.yahoo.document.restapi.resource.RestApi.handleInternal(RestApi.java:215)\n\tat com.yahoo.document.restapi.resource.RestApi.handle(RestApi.java:175)\n\tat com.yahoo.container.jdisc.ThreadedHttpRequestHandler.handle(ThreadedHttpRequestHandler.java:67)\n\tat com.yahoo.container.jdisc.ThreadedHttpRequestHandler.handleRequest(ThreadedHttpRequestHandler.java:80)\n\tat com.yahoo.container.jdisc.ThreadedRequestHandler$RequestTask.processRequest(ThreadedRequestHandler.java:189)\n\tat com.yahoo.container.jdisc.ThreadedRequestHandler$RequestTask.run(ThreadedRequestHandler.java:183)\n\tat java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)\n\tat java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)\n\tat java.base/java.lang.Thread.run(Thread.java:834)\n",
      "id": -15
    }
  ],
  "id": "id:db:system::7.230.4",
  "pathId": "/document/v1/db/system/docid/7.230.4"
}

Most annoyingly the POST operation (and the DocumentPut) silently ignores the problem. The PUT (DocumentUpdate) could also provide a more comprehensive error message.