hcloud: Add autocomplete support for bash and zsh

Currently one would need to manually run the command to generate
completion and insert it into `.bashrc`/`.zshrc` to get the
autocompletion to work. This patch will automatically generate
both docs and save them to correct position so it should continue
to work even if user changes the shell at a later stage.

(cherry picked from commit d23c357)

pkgs/development/tools/hcloud/default.nix

@@ -14,6 +14,19 @@ buildGoPackage rec {
 
   buildFlagsArray = [ "-ldflags=" "-w -X github.com/hetznercloud/cli/cli.Version=${version}" ];
 
+  postInstall = ''
+    mkdir -p \
+      $bin/etc/bash_completion.d \
+      $bin/share/zsh/vendor-completions
+
+    # Add bash completions
+    $bin/bin/hcloud completion bash > "$bin/etc/bash_completion.d/hcloud"
+
+    # Add zsh completions
+    echo "#compdef hcloud" > "$bin/share/zsh/vendor-completions/_hcloud"
+    $bin/bin/hcloud completion zsh >> "$bin/share/zsh/vendor-completions/_hcloud"
+  '';
+
   meta = {
     description = "A command-line interface for Hetzner Cloud, a provider for cloud virtual private servers";
     homepage = https://github.com/hetznercloud/cli;