Fixing GettAtt and Ref functions.

[jonjara]

Issue #, if available:

Description of changes: Apparently, Ref and GetAtt send model with only arn because its the primary identifier. Updating so the handlers can handler this scenario.

Also removing some properties from schema's based on feedback from discussions. I am removing Arn from readOnly because this conflicts with contract tests that prevent Create being called with readOnly properties, which does happen GetAtt is called in a create template. It's a bit intuitive..

The ArnUtils class should be shared between packages, I tried doing this but couldnt get maven to do what I wanted, so I am tabling this for later in the interest of time

Testing cfn submit and deployed these stacks

Parameters:
  Name:
    Type: String
Resources:
  TestCodeArtifactDomain:
    Type: 'AWS::CodeArtifact::Domain'
    Properties:
      DomainName: !Ref Name
Outputs:
  DomainOwner:
    Value: !GetAtt TestCodeArtifactDomain.DomainOwner
  Arn:
    Value: !Ref TestCodeArtifactDomain    

Parameters:
  Name:
    Type: String
  DomainName:
    Type: String    
Resources:
  TestCodeArtifacRepository:
    Type: 'AWS::CodeArtifact::Repository'
    Properties:
      RepositoryName: !Ref Name
      DomainName: !Ref DomainName

Outputs:
  Arn:
    Value: !Ref TestCodeArtifacRepository

  Admin:
    Value: !GetAtt TestCodeArtifacRepository.AdministratorAccount    

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