Use sas token for send downloads (#1157)

* Remove Url from SendFileModel

Url is now generated on the fly with limited lifetime.

New model houses the download url generated

* Create API endpoint for getting Send file download url

* Generate limited-life Azure download urls

* Lint fix

src/Core/Services/NoopImplementations/NoopSendFileStorageService.cs

@@ -26,5 +26,10 @@ namespace Bit.Core.Services
         {
             return Task.FromResult(0);
         }
+
+        public Task<string> GetSendFileDownloadUrlAsync(string fileId)
+        {
+            return Task.FromResult((string)null);
+        }
     }
 }