swagger: clarify the meaning of Image field in ContainerInspect endpoint

"Container's image" term is rather ambiguous: it can be both a name and an ID.

Looking at the sources[1], it's actually an image ID, so bring some clarity.

[1]: https://github.com/moby/moby/blob/a6a47d1a4944799ffbe3657d4dae68e0829a0dc6/daemon/inspect.go#L170

Signed-off-by: Nikolay Edigaryev <edigaryev@gmail.com>

api/swagger.yaml

@@ -5086,7 +5086,7 @@ paths:
                 x-nullable: true
                 $ref: "#/definitions/ContainerState"
               Image:
-                description: "The container's image"
+                description: "The container's image ID"
                 type: "string"
               ResolvConfPath:
                 type: "string"