Missing vital piece of information on the documentation

#### Overview of the Issue

In the documentation of the DTL builder, the description of the object DtlArtifact has a missing member, repository_name, which requires to have the private repository name.

#### Reproduction Steps

1. Go to https://www.packer.io/docs/builders/azure/dtl#dtlartifact
2. Notice there is only reference to artifact_name, artifact_id, parameters

As the repository_name is set to "public artifacts" in case that is not specified in the config file, the documentation states nothing about that member being available, and azure only says something along the lines "The ResourceId for the artifact is malformed"... it is very easy to spend a lot of time debugging this issue.

Start with the DTL builder documentation at the linked Azure page and inspect the DtlArtifact section, which currently lists artifact_name, artifact_id, and parameters. Document repository_name, including its private repository purpose and the default of "public artifacts" when omitted, then verify the rendered section reflects the available configuration member.

Written by the indexing model from the issue text.