feat: add unified release workflow with crates.io, Homebrew, and Dock…

[Zee2413]

…er publishing

Issue #, if available:

Description of changes:
Replaces the existing release.yml with a unified release workflow triggered via workflow_dispatch.

• Automates version bumping across all three Cargo.toml files (guard, guard-lambda, guard-ffi)
• Builds cross-platform binaries for linux, macOS, and Windows (x86_64, aarch64, i686) with backward-compatible asset names
• Creates GitHub Release with auto-generated release notes and all binary assets
• Publishes cfn-guard, cfn-guard-lambda, and cfn-guard-ffi to crates.io (after GitHub Release succeeds)
• Pushes versioned Docker image to ECR Public Gallery
• Opens Homebrew formula PR automatically with computed SHA256
• Includes dry run mode and skip flags for crates.io and Homebrew
• Replaces deprecated actions (upload-release-asset@v1, get-release@v1.3.2) with modern alternatives
• Removes publish_docker.yml and publish_tagged_docker.yml — Docker publishing is now consolidated in the release workflow
• Docker latest tag is now exclusively owned by the release workflow (no longer overwritten on every push to main)

Testing:

• screenshot of options for Run Workflow below
• successfully tested in public fork workflow which created the expected assets (releases)
  • Publish Docker to ECR expected to fail since the secrets were not available in public fork
  • Docker to ECR can be verified in aws-cloudformation repo after merge
• crates and homebrew steps to be verified in main repo after merge

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[deepfuriya]

LGTM