Phase 14 follow-up: Homebrew packaging

[dekobon]

Track shipping a Homebrew formula for git-remote-object-store so macOS
users can install via brew install rather than cargo install plus
manual +-form symlink creation.

Scope:

• Submit a formula to a tap (or homebrew-core once the project hits a
  version they accept).
• The formula installs all six binaries (git-remote-{s3,az}-{http,https},
  git-remote-object-store, git-lfs-object-store) and creates the
  git-remote-{s3,az}+{http,https} symlinks that git looks up by scheme.
• Ship release tarballs from the GitHub Release pipeline (already wired
  up in .github/workflows/release.yml for aarch64-apple-darwin).

Tracked as a Phase 14 follow-up per #14.