Add bash completion for `swarm join --availability`

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

contrib/completion/bash/docker

@@ -2963,6 +2963,10 @@ _docker_swarm_join() {
 			fi
 			return
 			;;
+		--availability)
+			COMPREPLY=( $( compgen -W "active drain pause" -- "$cur" ) )
+			return
+			;;
 		--token)
 			return
 			;;
@@ -2970,7 +2974,7 @@ _docker_swarm_join() {
 
 	case "$cur" in
 		-*)
-			COMPREPLY=( $( compgen -W "--advertise-addr --help --listen-addr --token" -- "$cur" ) )
+			COMPREPLY=( $( compgen -W "--advertise-addr --availability --help --listen-addr --token" -- "$cur" ) )
 			;;
 		*:)
 			COMPREPLY=( $( compgen -W "2377" -- "${cur##*:}" ) )