feat: add environment configuration files for frontend

[caponetto]

This pull request introduces a major refactor and enhancement to the frontend workspace's environment and build configuration. The changes standardize environment variable management across different environments, improve webpack configuration modularity, and make the development setup more robust and flexible. Key updates include the addition of a custom dotenv management utility, significant rewrites of webpack configs to leverage this utility, and improvements to local development and build processes. These changes are meant to be in sync with Model Registry.

Environment variable and dotenv management:

• Added a new config/dotenv.js utility to handle loading and expanding environment variables, supporting both root and nested project structures, and integrating with webpack via plugins.
• Updated all .env* files to include relevant variables for branding, deployment mode, and environment-specific settings, ensuring consistent configuration across development, production, and testing.

Webpack configuration refactor:

• Refactored webpack.common.js and webpack.dev.js to use the new dotenv utility, moving away from hardcoded paths and variables. This enables dynamic configuration based on environment variables and simplifies path management.
• Enhanced the webpack dev server setup with better proxy header handling, hot reloading, and improved output/logging for local development.

Build and asset handling improvements:

• Improved asset copying and handling in webpack, ensuring that images, favicons, locales, and other static files are correctly managed for all build targets.
• Updated babel configuration with presets for React, TypeScript, and targeted browsers, ensuring modern JS features are transpiled appropriately.

Documentation and developer experience:

• Updated README.md to clarify that the UI runs with mocked data by default and how to control backend connectivity via the environment.
• Added new words to the spell-check ignore list and updated style paths to support PatternFly extensions.

Other housekeeping:

• Removed .env from .gitignore to allow versioning of environment templates, and made minor cleanups to support the new structure.

These changes collectively make the frontend workspace more maintainable, configurable, and developer-friendly.

[paulovmr]

/ok-to-test

[paulovmr]

/lgtm

[ederign]

/approve
/lgtm

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ederign

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