add support for running validator in docker

[punkle]

No description provided.

[punkle]

fixes #116

[Copilot]

Pull request overview

This PR adds Docker support for the backstage-entity-validator, enabling users to run the validator in a containerized environment without needing to install Node.js or dependencies locally.

Changes:

• Adds a multi-stage Dockerfile for building and running the validator
• Creates GitHub Actions workflow for automated Docker image publishing to Docker Hub
• Adds Docker smoke tests to the CI pipeline to verify container functionality
• Documents Docker usage with examples in the README

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
README.md	Documents Docker usage with installation instructions and example commands
Dockerfile	Implements multi-stage build with node:20-alpine for optimized production image
.github/workflows/docker-publish.yml	Automates Docker image publishing on main branch pushes with version tagging
.github/workflows/ci.yml	Adds smoke tests validating Docker build and basic container functionality
.dockerignore	Excludes unnecessary files from Docker build context

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[Copilot]

Using @main for GitHub Actions is not recommended as it can lead to unexpected breaking changes. Pin to a specific version tag (e.g., @v4) to ensure reproducible builds.

[Xantier]

bump to current LTS

[punkle]

Done