Add basic bash completion for manifest command family

Because I was not able to figure out what could be legal values for
MANIFEST_LIST and MANIFEST, I do not offer any completion for these
values.
This could probably be refined.

Probably there are also sensible completions for
`manifest annotate --arch|--os|--variant`, but these are also not documented.

Signed-off-by: Harald Albers <github@albersweb.de>

Author: albers

contrib/completion/bash/docker

@@ -1146,6 +1146,7 @@ _docker_docker() {
 		*)
 			local counter=$( __docker_pos_first_nonflag "$(__docker_to_extglob "$global_options_with_args")" )
 			if [ "$cword" -eq "$counter" ]; then
+				__docker_client_is_experimental && commands+=(${experimental_client_commands[*]})
 				__docker_server_is_experimental && commands+=(${experimental_server_commands[*]})
 				COMPREPLY=( $( compgen -W "${commands[*]} help" -- "$cur" ) )
 			fi
@@ -3839,6 +3840,71 @@ _docker_swarm_update() {
 	esac
 }
 
+_docker_manifest() {
+	local subcommands="
+		annotate
+		create
+		inspect
+		push
+	"
+	__docker_subcommands "$subcommands" && return
+
+	case "$cur" in
+		-*)
+			COMPREPLY=( $( compgen -W "--help" -- "$cur" ) )
+			;;
+		*)
+			COMPREPLY=( $( compgen -W "$subcommands" -- "$cur" ) )
+			;;
+	esac
+}
+
+_docker_manifest_annotate() {
+	case "$prev" in
+		--arch|--os|--os-features|--variant)
+			return
+			;;
+	esac
+
+	case "$cur" in
+		-*)
+			COMPREPLY=( $( compgen -W "--arch --help --os --os-features --variant" -- "$cur" ) )
+			;;
+		*)
+			;;
+	esac
+}
+
+_docker_manifest_create() {
+	case "$cur" in
+		-*)
+			COMPREPLY=( $( compgen -W "--amend -a --help --insecure" -- "$cur" ) )
+			;;
+		*)
+			;;
+	esac
+}
+
+_docker_manifest_inspect() {
+	case "$cur" in
+		-*)
+			COMPREPLY=( $( compgen -W "--help --insecure --verbose -v" -- "$cur" ) )
+			;;
+		*)
+			;;
+	esac
+}
+
+_docker_manifest_push() {
+	case "$cur" in
+		-*)
+			COMPREPLY=( $( compgen -W "--help --insecure --purge -p" -- "$cur" ) )
+			;;
+		*)
+			;;
+	esac
+}
+
 _docker_node() {
 	local subcommands="
 		demote
@@ -5096,6 +5162,10 @@ _docker() {
 		wait
 	)
 
+	local experimental_client_commands=(
+		manifest
+	)
+
 	local experimental_server_commands=(
 		checkpoint
 		deploy