[gzhttp] Add supported decompress request body

[mirecl]

Add new feature from discussions #1001

[klauspost]

Please add and implement these options:

// AllowCompressedRequests will enable or disable RFC 7694 compressed requests.
// By default this is Disabled.
// See https://datatracker.ietf.org/doc/html/rfc7694
func AllowCompressedRequests(b bool) option {
	return func(c *config) {
		//....
	}
}

// SendAcceptEncoding will send Accept-Encoding on all responses as per RFC 7694.
// By default, none will be sent.
// Calling this with no parameters will send the currently supported encodings back.
// This does not affect which encodings are accepted.
func SendAcceptEncoding(enc ...string) option {
	return func(c *config) {
		//....
	}
}

While it would be really nice to have this enabled by default, I think the "zip-bomb" risk is too high.

[klauspost]

Just as an example AWS S3 "overloads" Content-Encoding on their uploads. in their terms it means the object should remain untouched and always return Content-Encoding: whatever when the object is downloaded. This change would be breaking for that if enabled by default.

[mirecl]

Just as an example AWS S3 "overloads" Content-Encoding on their uploads. in their terms it means the object should remain untouched and always return Content-Encoding: whatever when the object is downloaded. This change would be breaking for that if enabled by default.

@klauspost

• AllowCompressedRequests - should help solve this problem
• zstdReader - i suggest limiting ourselves to gzip support for now

[mirecl]

@klauspost, all tasks done! Thank you very much for your patience and tips)

[klauspost]

Cool. Giving it a final review! Thanks for the contribution!