api/swagger: update /containers/{id}/wait "condition" parameter to match code

This patch updates the swagger, and:

- adds an enum definition to document valid values (instead of describing them)
- updates the description to mention both "omitted" and "empty" values (although
  the former is already implicitly covered by the field being "optional" and
  having a default value).

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

api/swagger.yaml

@@ -7038,9 +7038,14 @@ paths:
         - name: "condition"
           in: "query"
           description: |
-            Wait until a container state reaches the given condition, either
-            'not-running' (default), 'next-exit', or 'removed'.
+            Wait until a container state reaches the given condition.
+
+            Defaults to `not-running` if omitted or empty.
           type: "string"
+          enum:
+            - "not-running"
+            - "next-exit"
+            - "removed"
           default: "not-running"
       tags: ["Container"]
   /containers/{id}: