feat: add gzip as content-encoding

The engine is introducing a new feature allowing to optionally compress request
payloads (ie. POST/PUT body, http or https).

To test it:

Perform a `saveObject` with the content encoded with GZIP
Don't forget to add: `"Content-Encoding: gzip"` as a header.

We will discuss a specification for a more detailed implementation.
Like adding a `enableGZIP` flag in client's configuration.