chore: Bundle js files, remove jQuery, and static libs

[fsbraun]

Description

Convert JavaScript in django-filer from jQuery to ES modules and vanilla JS, bundle scripts with webpack, remove static legacy libraries, and modernize the build and lint workflows.

New Features:

• Introduce webpack.config.js and Gulp “bundle” task to produce ES module bundles for filer and admin-file-widget scripts.

Enhancements:

• Rewrite all JS addons and base scripts as ES modules using vanilla JavaScript instead of jQuery.
• Refactor package.json to define build, watch, lint and test scripts and update Gulpfile to invoke webpack and ESLint.
• Update Django admin widgets and templates to load the new bundled JS instead of individual static libs.

Build:

• Integrate webpack bundling into the Gulp workflow, enabling source maps in debug mode and minification in production.

CI:

• Replace Flake8 with Ruff for pre-commit linting and add ESLint in CI pipelines.

Chores:

• Remove obsolete static JS libraries (jQuery, jquery-ui, mediator, dropzone, etc.) from the repo and templates.

Related resources

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Checklist

• I have opened this pull request against master
• I have added or modified the tests when changing logic
• I have followed the conventional commits guidelines to add meaningful information into the changelog
• I have read the contribution guidelines and I have joined #workgroup-pr-review on
  Slack to find a “pr review buddy” who is going to review my pull request.

[sourcery-ai]

Sorry @fsbraun, your pull request is larger than the review limit of 150000 diff characters

[vinitkumar]

Looks good to me. Let's get this merged and released 🚢 🚀