Add Homebrew bottle support via GoReleaser

[Copilot]

Homebrew formula currently builds from source, requiring Go compiler. This adds bottle (prebuilt binary) distribution via GoReleaser's native Homebrew integration.

Changes

• .goreleaser.yml: Added brews section configuring bottle creation

  • Repository: DefangLabs/homebrew-defang
  • Shell completions generated at install time via defang completion {bash,zsh,fish}
  • Commit author: defang-bot

• .github/workflows/go.yml:

  • Added HOMEBREW_ACTION_TRIGGER_TOKEN to GoReleaser env
  • Removed manual formula update trigger (GoReleaser now handles this)

Technical Notes

GoReleaser will automatically:

1. Create bottles from signed/notarized macOS universal binaries
2. Generate formula with bottle references
3. Push to tap repository on release

Users get prebuilt binaries instead of 2-5 minute compile. Go compiler no longer required as dependency.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Create homebrew bottle for the Defang CLI binaries</issue_title>
<issue_description>Current brew needs Go compiler because it builds from source. This should not be necessary: we should ship the prebuilt and signed binaries. This should be done ideally with Goreleaser during the release workflow.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create homebrew bottle for the Defang CLI binaries #1888

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