Handle invalid repository names gracefully

What does this MR do and why?

Handle invalid repository names gracefully

for the POST /container_registry_event/events endpoint.

Before this fix, the endpoint would return a 500 status code.

References

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• Related to Registry event endpoint raises a 500 when the r... (#350523 - closed)

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Before	After

How to set up and validate locally

1. Save the following event payload into a file locally, e.g. bad-event.json. Note the "repository":"unknown-repository" is the problem here.

{
   "events": [
      {
         "id": "1aa3d563-84f0-4c24-a4d7-069700f9f73f",
         "timestamp": "2022-01-18T12:53:32.093331+11:00",
         "action": "push",
         "target": {
            "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
            "size": 528,
            "digest": "sha256:5e604d3358ab7b6b734402ce2e19ddd822a354dc14843f34d36c603521dbb4f9",
            "length": 528,
            "repository": "unknown-repository",
            "url": "http://registry.test:5000/v2/unknown-repository/manifests/sha256:5e604d3358ab7b6b734402ce2e19ddd822a354dc14843f34d36c603521dbb4f9",
            "tag": "alpine"
         },
         "request": {
            "id": "a0f4d5a5-424a-4dca-86d1-99e6477f7b37",
            "addr": "172.16.123.1:57699",
            "host": "registry.test:5000",
            "method": "PUT",
            "useragent": "docker/20.10.11 go/go1.16.9 git-commit/847da18 kernel/5.10.76-linuxkit os/linux arch/amd64 UpstreamClient(Docker-Client/20.10.11 \\(darwin\\))"
         },
         "actor": {},
         "source": {
            "addr": "Jaimes-MacBook-Pro.local:5000",
            "instanceID": "9c9280d4-4e0d-4c4b-b25a-af1b22b67b1a"
         }
      }
   ]
}

2. Call the /container_registry_event/events endpoint via curl

export ns='notifications_secret'
curl -XPOST --header "Authorization: $ns" --header "Content-Type: application/vnd.docker.distribution.events.v1+json" "http://gdk.test:3000/api/v4/container_registry_event/events" --upload-file bad-event.json
{"message":"Invalid repository path"}%