update central resources Readme

All Submissions:

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• [YES] Have you added an explanation of what your changes do and why you'd like us to include them?
• [YES] I have updated the documentation accordingly.
• [YES] My code follows the code style of this project.

Current Behavior or Linked Issues

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objectId filed is not present - issue 261

• az ad sp list command do not return objectId field, made changes to fetch id instead of objectId
• fetched appId field before using it in subsequent steps
• tested changes by deploying service-principal module using terraform and Contributer role assignment key vault and container registry is successful with changes.