Create goreleaser process for building CLI and brew pushing

[mkysel]

Add GoReleaser-driven CI to build xmtpd-cli and publish tagged releases to GitHub Releases and the xmtp/homebrew-tap Homebrew cask

• Add a GitHub Actions workflow in release-goreleaser.yaml that runs on tag pushes matching v*, pushes to main, pull requests, and manual dispatch, performs snapshot builds for non-tag events, publishes releases on tag pushes, and uploads dist/** artifacts.
• Introduce GoReleaser v2 config in .goreleaser.yaml to build xmtpd-cli for linux/darwin on amd64/arm64 with CGO disabled, embed version metadata via ldflags, package archives as .zip and .tar.gz with shell completions and LICENSE, generate checksums, and update the Homebrew cask in xmtp/homebrew-tap.
• Ignore the build output directory by adding dist/ to .gitignore.

📍Where to Start

Start with the workflow definition in release-goreleaser.yaml, then review the build and publishing configuration in .goreleaser.yaml.

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Macroscope summarized 4f3c214.

[graphite-app]

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