add egctl formula

egctl is a command line tool to provide additional functionality for Envoy Gateway users, add a formula make it easier for brew users to install it.

Signed-off-by: zirain <[email protected]>

Formula/e/egctl.rb

@@ -0,0 +1,31 @@
+class Egctl < Formula
+  desc "Command-line utility for operating Envoy Gateway"
+  homepage "https://gateway.envoyproxy.io/"
+  url "https://github.com/envoyproxy/gateway/archive/refs/tags/v1.0.2.tar.gz"
+  sha256 "05406182dc165513925cf60722582613d4de9ea789d60e014e6da456bb229f65"
+  license "Apache-2.0"
+  head "https://github.com/envoyproxy/gateway.git", branch: "main"
+
+  livecheck do
+    url :stable
+    strategy :github_latest
+  end
+
+  depends_on "go" => :build
+
+  def install
+    ldflags = %W[
+      -s -w
+      -X github.com/envoyproxy/gateway/internal/cmd/version.envoyGatewayVersion=#{version}
+      -X github.com/envoyproxy/gateway/internal/cmd/version.gitCommitID=#{tap.user}
+    ]
+    system "go", "build", *std_go_args(ldflags:), "./cmd/egctl"
+
+    generate_completions_from_executable(bin/"egctl", "~")
+  end
+
+  test do
+    output = shell_output("#{bin}/egctl version --remote=false")
+    assert_equal "envd: v#{version}", output.strip
+  end
+end