Fix Mermaid diagrams

Changed

• feat(BREAKING CHANGE): Throw an error in case the cwd input is absolute, because the action only has access to the repository files
• chore: Use Docker action instead of Node.js action in order to install Chromium and Puppeteer
• chore: Use Pnpm instead of NPM
• chore: Move dependencies to devDependencies, because in runtime the action uses only the bundled code, and it installs the mermaid dependencies by itself in the Docker image. This is because the @tid-xcut libraries are in a private repository, and the action cannot install them in the Docker image. Some fixes are applied to the bundled code to make it work in the Docker image.

Fixed

• fix: Generate mermaid diagrams in the Confluence page

Added

• docs: Add automation notice to Confluence pages containing the action docs
• test: Add mermaid diagram to readme.md file, and test that it has been synced to Confluence in E2E tests