fshttp: add --dump curl for dumping HTTP requests as curl commands

docs/content/docs.md

@@ -3278,6 +3278,10 @@ The available flags are:
 - `mapper` dumps the JSON blobs being sent to the program supplied with
   `--metadata-mapper` and received from it. It can be useful for debugging
   the metadata mapper interface.
+- `curl` dumps the HTTP request as a `curl` command. Can be used with
+  the other HTTP debugging flags (e.g. `requests`, `bodies`). By
+  default the auth will be masked - use with `auth` to have the curl
+  commands with authentication too.
 
 ## Filtering