Update Data Factory authentication to use managed identity to access Azure Files (airlock)

The Data Factory connector for Azure Files now supports using managed identities, including user-assigned managed identities (UAMI). The current implementation uses legacy shared key access with a connection string stored in Key Vault.

Doc ref: https://learn.microsoft.com/azure/data-factory/connector-azure-file-storage?tabs=data-factory#user-assigned-managed-identity-authentication

- [x] Remove Azure Files connection strings from Key Vault.
- [ ] Update Azure File Shares authentication to allow the user-assigned managed identity for ADF to read and write files.
- The UAMI needs the `Storage File Data Privileged Contributor` role
- [ ] Update the Linked Service definition for the generic File Share to use user-assigned managed identity.
- [x] Remove the Key Vault Linked Service from ADF because it was only used to access the connection string secret.
- [x] Turn off access key authentication on all storage accounts.