[Do Not Merge] Adding sample code for auth using azure credentials.

[mbhaskar]

Sample code to demo the AAD based authentication

• Step 1) Add azure identity dependency
  Example:
  
  com.azure
  azure-identity
  1.2.2
  

• Step 2) Define environment variables as per requirement as defined here
  https://docs.microsoft.com/en-us/java/api/overview/azure/identity-readme?view=azure-java-stable#service-principal-with-secret
  And create a default credential as required
  DefaultAzureCredential credential = new DefaultAzureCredentialBuilder().build();
  and pass it to the CosmosClientBuilder() using .credential()

    @Bean
    public CosmosClientBuilder cosmosClientBuilder() {
        DefaultAzureCredential credential = new DefaultAzureCredentialBuilder().build();
        return new CosmosClientBuilder()
                       .endpoint(properties.getUri())
                       .credential(credential)
                       .directMode(directConnectionConfig);
    }

Note:
Make sure you use an existing database and container and supply them to the config accordingly as RBAC auth may be able work only on document operations.

** Do not merge this code into this sample until we create a new sample for demonstrating above and then we can put this code there