@VisibleForTesting
  public List<String> getRepoTags() {
    return repoTags;
  }
JSON Template for a loadable Docker Manifest entry. The RepoTags property requires a tag; i.e. if
a tag is missing, it explicitly should use "latest".

<p>Note that this is a template for a single Manifest entry, while the entire Docker Manifest
should be {@code List<DockerManifestEntryTemplate>}.

<p>Example manifest entry JSON:

<pre>{@code
{
  "Config":"config.json",
  "RepoTags":["repository:tag"]
  "Layers": [
    "eb05f3dbdb543cc610527248690575bacbbcebabe6ecf665b189cf18b541e3ca.tar.gz",
    "ba7c544469e514f1a9a4dec59ab640540d50992b288adbb34a1a63c45bf19a24.tar.gz",
    "15705ab016593987662839b40f5a22fd1032996c90808d4a1371eb46974017d5.tar.gz"
  ]
}
}</pre>

@see <a href="https://github.com/moby/moby/blob/master/image/tarexport/load.go">Docker load
    source</a>
jib-core/src/main/java/com/google/cloud/tools/jib/docker/json/DockerManifestEntryTemplate.java