Add 'ancestor' ps filter for image

Makes it possible to filter containers by image, using
--filter=ancestor=busybox and get all the container running busybox
image and image based on busybox (to the bottom).

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

docs/reference/commandline/ps.md

@@ -50,6 +50,7 @@ The currently supported filters are:
 * name (container's name)
 * exited (int - the code of exited containers. Only useful with `--all`)
 * status (created|restarting|running|paused|exited)
+* ancestor (`<image-name>[:<tag>]`,  `<image id>` or `<image@digest>`) - filters containers that were created from the given image or a descendant.
 
 
 #### Label

man/docker-ps.1.md

@@ -41,6 +41,8 @@ the running containers.
                           status=(created|restarting|running|paused|exited)
                           name=<string> - container's name
                           id=<ID> - container's ID
+                          ancestor=(<image-name>[:tag]|<image-id>|<image@digest>) - filters containers that were
+                          created from the given image or a descendant.
 
 **-l**, **--latest**=*true*|*false*
    Show only the latest created container, include non-running ones. The default is *false*.