Add GZIP compression filter for response bodies

[DennSel]

Implement a CompressionFilter that compresses HTTP response bodies using GZIP encoding to reduce bandwidth usage and improve transfer speeds for clients.

Why:

• Real-world production feature
• Reduces bandwidth by ~60-80%
• Standard HTTP practice (browsers auto-decompress)

What:
A filter that:

• Checks client's Accept-Encoding: gzip header
• Compresses response body using java.util.zip.GZIPOutputStream
• Sets Content-Encoding: gzip header
• Can be disabled via configuration