introduce create_host_path

Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

schema/compose-spec.json

@@ -408,7 +408,8 @@
                   "bind": {
                     "type": "object",
                     "properties": {
-                      "propagation": {"type": "string"}
+                      "propagation": {"type": "string"},
+                      "create_host_path": {"type": "boolean"}
                     },
                     "additionalProperties": false,
                     "patternProperties": {"^x-": {}}

spec.md

@@ -1811,6 +1811,8 @@ expressed in the short form.
 - `read_only`: flag to set the volume as read-only
 - `bind`: configure additional bind options
   - `propagation`: the propagation mode used for the bind
+  - `create_host_path`: create a directory at the source path on host if there is nothing present. 
+    Do nothing if there is something present at the path. This is automatically implied by short syntax.
 - `volume`: configure additional volume options
   - `nocopy`: flag to disable copying of data from a container when a volume is created
 - `tmpfs`: configure additional tmpfs options