feat: support preview and release candidate channels

[thisislawatts]

This PR introduces a refactor of the GitHub Actions workflows to streamline the build and deployment process across different distribution channels (stable, preview, and rc).

Rationale:

• This refactor simplifies long-term maintenance by consolidating build logic into a single template.
• Distribution channels are critical for testing and releasing, and this change ensures workflows stay aligned with the evolving release process.
• Reduces redundancy and enforces consistency across distribution workflows.

Key Changes:

Workflow Generation Overhaul:

Replaced build.yml with dynamically generated workflows (stable.yml, preview.yml, and rc.yml) based on the new _templates/distribution-channel.yml.erb template.
This change allows more consistent management of distribution channels, reducing duplication and manual edits.

Template Update:

The build.yml.erb template is renamed to distribution-channel.yml.erb to reflect its expanded responsibility of handling multiple channels.
Logic within the template supports distribution-specific postfixes (-preview, -rc), aligning with Snyk CLI release channels.

Ruby Build Script Update (build.rb):

The build script now dynamically generates workflows for each distribution channel by iterating over a distribution_map.
Ensures consistent workflow creation, reducing human error and automating workflow generation for new channels.
Generated Workflow Changes:

preview.yml and rc.yml are added, mirroring the existing stable.yml but adapted for the respective distribution channels.
stable.yml replaces the previous build.yml, maintaining parity with prior stable builds.

Testing:

• Verified that workflows generate correctly and trigger builds for all channels (stable, preview, rc).
• Confirmed Docker image tags reflect the appropriate distribution postfix during the build process.