images: print hint when invoking "docker images" with ambiguous argument

The `docker images` top-level subcommand predates the `docker <object> <verb>`
convention (e.g. `docker image ls`), but accepts a positional argument to
search/filter images by name (globbing). It's common for users to accidentally
mistake these commands, and to use (e.g.) `docker images ls`, expecting
to see all images, but ending up with an empty list because no image named
"ls" was found.

Disallowing these search-terms would be a breaking change, but we can print
and informational message to help the users correct their mistake.

Before this patch:

    docker images ls
    REPOSITORY   TAG       IMAGE ID   CREATED   SIZE

With this patch applied:

    docker images ls
    REPOSITORY   TAG       IMAGE ID   CREATED   SIZE

    No images found matching "ls": did you mean "docker image ls"?

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

cli/command/image/testdata/list-command-ambiguous.golden

@@ -0,0 +1,2 @@
+
+No images found matching "ls": did you mean "docker image ls"?