kubevela: add completions

Closes #111253.

Signed-off-by: Sean Molenaar <1484494+SMillerDev@users.noreply.github.com>
Signed-off-by: BrewTestBot <1589480+BrewTestBot@users.noreply.github.com>

Formula/kubevela.rb

@@ -27,6 +27,8 @@ class Kubevela < Formula
     ]
 
     system "go", "build", *std_go_args(output: bin/"vela", ldflags: ldflags), "./references/cmd/cli"
+
+    generate_completions_from_executable(bin/"vela", "completion", shells: [:bash, :zsh], base_name: "vela")
   end
 
   test do