RELIC: Enhance Support for Serving Static Files

[klkucaj]

Is your feature request related to a problem? Please describe.
The current support for serving static files is limited or lacks flexibility in handling various use cases, such as caching, content negotiation, or serving files from custom directories. Enhancing this functionality can improve performance and make the framework more versatile.

Describe the solution you'd like
Enhance static file support by:

• Adding better caching mechanisms (e.g., ETag, Last-Modified, Cache-Control headers).
• Allowing configuration for serving files from custom directories.
• Supporting partial content responses (e.g., Range requests) for large files.
• Improving MIME type handling for different file extensions.

Describe alternatives you've considered

• Using an external file server to handle static files. While feasible, this introduces additional complexity and dependencies for applications that need to serve static assets.

Additional context
Enhanced static file support will align the framework with modern web application needs and simplify serving common assets like images, scripts, and styles.