Migrated to use DefaultCredential if possible

[backwind1233]

Tracked in [Epic] improvements of azure-spring-boot-samples

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now our samples don't have a unified template or approach to run.
Samples are configured with different authentication methods, likes accesskey, service principal, connectionString.

📄Spring Cloud Azure Samples improvement Track

Sample Name	defaultCredential
aad-resource-server	DONE
aad-resource-server-by-filter	DONE
aad-resource-server-by-filter-stateless	DONE
aad-resource-server-obo	DONE
aad-web-application	DONE
aad-web-application-and-resource-server	DONE
aad-b2c-web-application	DONE
aad-b2c-resource-server	DONE
spring-security	DONE
azure-appconfiguration-conversion-sample-complete	NA
azure-appconfiguration-conversion-sample-initial	NA
azure-appconfiguration-sample	NA
feature-management-sample	NA
feature-management-web-sample	NA
azure-cloud-foundry-service-sample	NA
spring-cloud-azure-data-cosmos-sample	DONE
spring-cloud-azure-cosmos-sample	DONE
cosmos-multi-database-multi-account	DONE
cosmos-multi-database-single-account	DONE
eventhubs-integration	DONE
spring-cloud-azure-sample-eventhubs-kafka	DONE
eventhubs-binder	DONE
eventhubs-multibinders	DONE
run-with-command-line-server-side	NA
run-with-command-line-client-side	NA
keyvault-certificates-client-side	NA
keyvault-certificates-server-side	NA
single-property-source	DONE
multiple-property-source	DONE
servicebus-jms-queue	DONE
servicebus-jms-topic	DONE
servicebus-queue-binder	DONE
servicebus-multibinders	DONE
servicebus-topic-binder	DONE
multiple-namespaces	DONE
single-namespace	DONE
storage-blob-sample	DONE
storage-file-sample	NA
storage-queue-operation	DONE
storage-queue-integration	DONE

[saragluna]

Why is storage file not applicable?

[saragluna]

Closing this now.