feat: Updated documentation, workflow streamlining, github pages added

[ric-v]

This pull request introduces significant improvements to project documentation and the extension publishing workflow for the PostgreSQL Explorer VS Code extension. It adds comprehensive new documentation files for both Copilot and the Marketplace, updates the publishing workflow for better version management and reliability, and configures a custom documentation domain.

Documentation Enhancements:

• Added .github/copilot-instructions.md with a detailed technical overview for AI Copilot integration, including project architecture, command patterns, helper utilities, styling, and development workflow.
• Added MARKETPLACE.md with a richly formatted, user-focused overview highlighting key features, screenshots, usage instructions, and resources for the extension.

Publishing Workflow Improvements:

• Refactored .github/workflows/publish.yml to:
  • Ensure full git history is available during CI builds.
  • Switch dependency management from Yarn to npm for consistency and reliability.
  • Add a step to extract and verify the version from git tags, warning if the tag and package.json versions do not match.
  • Simplify and clarify the packaging and publishing steps, explicitly naming the VSIX file and using npx for tool invocation. [1] [2]
  • Remove unnecessary version bumping and git commit steps, making the workflow tag-driven only.
• The workflow is now triggered only on tag pushes (v*) or manual dispatch, not on every push to main.

Documentation Hosting:

• Added a docs/CNAME file to configure the documentation site to use the custom domain yape.astrx.dev.