aws: add a basic ecr describe-images wrapper

[ibodrov]

Running tasks/aws/examples/ecr/concord.yml:

> concord run
Starting...
15:07:33.142 [main] Image Details: [ {
  "registryId" : "742982124480",
  "repositoryName" : "foo",
  "imageDigest" : "sha256:c49527020d9f72c711eb9ec89ae6162ddd88abebb69b79967c72b1ac56b60769",
  "imageTags" : [ "latest" ],
  "imageSizeInBytes" : 153448492,
  "imagePushedAt" : 1718737639.000000000,
  "imageScanStatus" : null,
  "imageScanFindingsSummary" : null,
  "imageManifestMediaType" : "application/vnd.docker.distribution.manifest.v2+json",
  "artifactMediaType" : "application/vnd.docker.container.image.v1+json",
  "lastRecordedPullTime" : null
} ]
...done!