Provide initial ACR Track 2 swagger to feature crew

[annelo-msft]

Per #2478, @jeremymeng will be working on correctness of the swagger file and working with the service team to get it checked into the azure-rest-api-spes repo. This work item is to create the initial shape of the file, per the API design reviewed by the arch board in the first ACR arch board introduction meeting.

[annelo-msft]

@jeremymeng @AlexGhiondea FYI