Support Custom Compression Settings in BackendTrafficPolicy

**Description**
Currently, Envoy Gateway's compression configuration only allows users to specify the compressor type (Gzip, Brotli, or Zstd) without any ability to customize compression parameters. Users cannot configure important settings like compression level, window size, chunk size, or algorithm-specific options that could significantly impact:
* Compression ratio vs CPU usage trade-offs
* Memory consumption during compression
* Performance characteristics for specific workload types

Another cool feature could be the ability to filter file types to be compressed, but I guess that could be done out of the scope of this directly in a filtering policy.

**Proposed Solution**
Extend the Compression API in BackendTrafficPolicy to support compressor-specific configuration fields

**Related**
PR: #8301
Envoy Compression Filters:
[gzip](https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/compression/gzip/compressor/v3/gzip.proto#extension-envoy-compression-gzip-compressor), [brotli](https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/compression/brotli/compressor/v3/brotli.proto#extension-envoy-compression-brotli-compressor), [zstd](https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/compression/zstd/compressor/v3/zstd.proto#extension-envoy-compression-zstd-compressor)