Support AWS profile when specifying bucket storage credentials

docs/clearml.conf

@@ -92,6 +92,8 @@ sdk {
             # Specify explicit keys
             key: ""
             secret: ""
+            # Specify profile
+            profile: ""
             # Or enable credentials chain to let Boto3 pick the right credentials. 
             # This includes picking credentials from environment variables, 
             # credential file and IAM role using metadata service. 
@@ -103,6 +105,7 @@ sdk {
 
             credentials: [
                 # specifies key/secret credentials to use when handling s3 urls (read or write)
+                # Note that all all fields in the global s3 config section are supported here
                 # {
                 #     bucket: "my-bucket-name"
                 #     key: "my-access-key"