Generate and install shell completions (#29)

Signed-off-by: Mohamed Hazem Abbas <mohamed.abbas@thoughtworks.com>

Author: CVirus

.github/workflows/homebrew.yml

@@ -45,6 +45,7 @@ jobs:
           install: |
             libexec.install Dir["*"]
                 bin.install_symlink libexec/"localstack"
+                generate_completions_from_executable(bin/"localstack", "completion")
 
           # Custom test command for your formula so you can run `brew test`.
           # Optional - string
@@ -60,4 +61,4 @@ jobs:
           target_darwin_amd64: true
           target_darwin_arm64: true
           target_linux_amd64: true
-          target_linux_arm64: true
+          target_linux_arm64: true