Doc: Clarify HTTP web compression vs HTTP block compression

[kavirajk]

Since CH 25.11, the enable_http_compression setting is default in ClickHouse,

Which leads to two different types of compression when using HTTP.

1. HTTP web compression - based on HTTP headers (whole response)
2. ClickHouse block compression

(1) is what general HTTP client understand (e.g: curl)
(2) is better for better for better compression.

The problem is sometimes user end up using both. But (2) needs custom code to decompress (via compress=1) query param.

The goal for this issue to document this behavior public.

[bobrik]

The problem is sometimes user end up using both.

And sometimes neither! I'm getting raw responses for CompressionGZIP, presumably because enable_http_compression defaults to zero on older versions of ClickHouse.