Switch release workflow to dynamic vcs

[ank1m]

GitHub Issue: #318

Description

This PR organizes the GitHub Actions workflows for testing, gating, and building new release.

Trigger Workflows

• test-on-push.yml
  Runs unit tests and linting on every push to any branch. Ensures baseline correctness for all commits.
• test-on-pr.yml
  Runs tests on pull requests to validate changes before merging.
• test-build-on-pr.yml
  Runs tests and performs a Docker build (without pushing) for PRs when build-relevant files change. Helps catch build/runtime issues early.
• build-release-candidate.yml
  Builds and publishes Docker images for release candidate (RC) tags. Triggered from release/* branches during the release cycle.
• build-release.yml
  Handles final release builds on merge to main. Produces and publishes the official Docker image, drafts GitHub release with notes, and create auto-PR for back-merge from main to develop.

Reusable Workflows

• reusable-tests.yml
  Shared test and linting workflow used across push and PR pipelines.
• reusable-docker.yml
  Contains Docker build and push logic. Supports both RC and final release builds.
• reusable-gate.yml
  Provides validation and gating logic (e.g., branch naming, release version rules).

Local test steps

See next section

Overview of integration done

• All workflows were validated in batchee and casper repositories. They confirms that workflows are ready for integration into the stitchee repository.
• The stitchee docker image was built locally and tested in local Harmony.

PR Acceptance Checklist

• Unit tests added/updated and passing
• Integration testing completed
• CHANGELOG.md updated
• Documentation updated (if needed)
• Breaking changes documented (if any)

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📚 Documentation preview 📚: https://stitchee--368.org.readthedocs.build/en/368/