hpack: request with empty/quotes as header value.

[RomanBelozerov]

Scope

For h2 request with headers:

[
  (":authority", "example.com"),
  (":path", "/"),
  (":scheme", "https"),
  (":method", "GET"),
  ('x-my-hdr', '""')  # empty/quotes as header value
]

AR: response with 400 status code. But for http1 Tempesta forwards request upstream.
ER: Tempesta forwards request upstream.

A field value MUST NOT start or end with an ASCII whitespace character (ASCII SP or HTAB, 0x20 or 0x09).

RFC 9113 8.2.1

Testing

Please add tests in http2_general and http_general for empty/quotes as header value in request/response.