Migration cleanup

[dshevtsov]

This pull request makes significant updates to repository automation and configuration, primarily focusing on simplifying workflows, updating deployment logic, and cleaning up linter and environment files. The changes streamline CI/CD processes, remove unused scripts and configurations, and introduce new validation and commenting workflows for pull requests.

Workflow and CI/CD updates:

• Removed several legacy workflow files including publish.yml, github-pages.yml, index.yml, lint.yml, and test-pull-request.yml, consolidating and simplifying CI/CD pipeline management. [1] [2] [3] [4] [5]
• Updated deployment workflows: deploy.yml now defaults to production deployments and uses a more robust input handling for environment variables; stage.yml is renamed to "Staging" and hardcodes the environment to stage. (Fca7e651L1, [1] [2] [3]
• Changed references in workflow calls to use the commerce-contributor repository instead of commerce-php, aligning with new automation sources.

Linting and configuration cleanup:

• Removed custom linter configuration files for Markdown and YAML, as well as the metadata schema for documentation, indicating a move to default or external linting standards. [1] [2] [3]
• Deleted the .github/linters/.markdownlint.yml reference from .markdownlint.yml, further cleaning up linter configuration.
• Removed the .github/super-linter.env file, eliminating custom environment settings for super-linter.

Environment and script cleanup:

• Deleted the .env.example file, removing unused example environment variables.
• Removed the obsolete script .github/scripts/get-path-prefix.js, which was previously used to validate and extract the Gatsby pathPrefix.

Enhancements to pull request automation:

• Added new workflows for PR validation (pr-validation.yml) and PR comment automation (pr-comment.yml), improving feedback for contributors by automatically commenting on PRs with lint warnings. [1] [2]

Documentation and template updates:

• Updated the PR template to clarify references to the public Commerce codebase instead of Magento Open Source.
• Improved dependabot.yml to assign all npm PRs to a specific user and changed the update schedule to weekly.