Describe the feature

Introduces a new secret provider for Azure Key Vault in the FlowSynx application. It includes the implementation of the AzureKeyVaultSecretProvider class and its configuration options. The ServiceCollectionExtensions class is updated to register the new provider as a singleton service. Additionally, the project file is modified to include necessary Azure SDK package references, and the AzureKeyVaultConfiguration class is created to manage configuration properties for the Azure Key Vault.