Prior to this commit, HTTP responses without body (response status 204
or 304, Content-Length: 0) were handled properly by RestTemplates. But
some other cases were not properly managed, throwing exceptions for
valid HTTP responses.
This commit better handles HTTP responses, using a response wrapper that
can tell if a response:
* has no message body (HTTP status 1XX, 204, 304 or Content-Length:0)
* has an empty message body
This covers rfc7230 Section 3.3.3.
Issue: SPR-8016
b6675b6167