Add support for setting mode on files applied by the agent

docs/clearml.conf

@@ -481,6 +481,7 @@ sdk {
 #  target_format: format used to encode contents before writing into the target file. Supported values are json,
 #                 yaml, yml and bytes (in which case the file will be written in binary mode). Default is text mode.
 #  overwrite: overwrite the target file in case it exists. Default is true.
+#  mode: set the file mode after writing. use an integer value or a string (e.g. 600 / 777 etc.)
 #
 # Example:
 #   files {