Lib Updates, Documentation Revisions, and Cleanup

[dividehex]

    This update focuses on modernizing the frontend by updating
    outdated Node packages, removing deprecated dependencies, and
    refreshing the documentation. The existing Node packages were
    significantly outdated, leading to frequent dependabot-triggered
    pull requests. Additionally, some development-only packages that
    have long been abandoned were removed. The documentation, which
    was also outdated, has been revised.

    Here is a summary of the changes:
    * Removed Gulp (considering using Parcel in the future).
    * Removed Bower and migrated frontend package management
      to npm.
    * Added a JavaScript script to copy frontend packages to
      the static/lib directory.
    * Updated ESLint and converted the configuration to the new
      format.
    * Removed the start.sh Docker entry script in favor of calling
      Gunicorn directly.
    * Refactored the Dockerfile for better readability and pinned
      the Node.js version inside the Docker image.
    * Pinned all components to Node.js v18.20.4. This version is the
      latest minor/patch release in the v18 series and aligns with
      the version used in Auth0. When v20 or above becomes available
      in Auth0, we will update all IAM-related Node.js components
      accordingly.
    * Excluded external frontend dependencies from pre-commit linting.
    * Refactored tox.ini to reduce redundancy in tox environments.
    * Pinned the Node version in tox.
    * Overhauled the README.md.
    * Updated the dashboard screenshot with a more current image.
    * Overhauled the Mermaid diagram to reflect the current state
      of the SSO Dashboard infrastructure.

[eduvic-mozilla]

Nitpicks, nothing to block approval