Quick fix for #11349 : Add support for generic options config value

Allow setting additional parameters at borg invocation time

Inspired from the duplicity handler's options variable

Quick fix for #11349 (closed)

examples/example.borg

@@ -11,6 +11,13 @@
 ## destination host and user.
 ##
 
+## passed directly to borg commands, e.g. to use a particular remote
+## borg executable (here: 'borg12'), set this to:
+## options = --remote-path=borg12
+##
+## Default:
+# options =
+
 ## default is 0, but set to 19 if you want to lower the priority.
 ## an example setting would be:
 ## nicelevel = 19