Add zsh completion scripts

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>

zsh-completions/_proxmox-backup-manager

@@ -0,0 +1,13 @@
+#compdef _proxmox-backup-manager() proxmox-backup-manager
+
+function _proxmox-backup-manager() {
+    local cwords line point cmd curr prev
+    cworkds=${#words[@]}
+    line=$words
+    point=${#line}
+    cmd=${words[1]}
+    curr=${words[cwords]}
+    prev=${words[cwords-1]}
+    compadd -- $(COMP_CWORD="$cwords" COMP_LINE="$line" COMP_POINT="$point" \
+        proxmox-backup-manager bashcomplete "$cmd" "$curr" "$prev")
+}