BUG/MEDIUM: h3: trim whitespaces when parsing headers value

BUG/MEDIUM: h3: trim whitespaces when parsing headers value

Remove any leading and trailing whitespace from header field values
prior to inserting a new HTX header block. This is done when parsing a
HEADERS frame, both as headers and trailers.

This must be backported up to 2.6.

(cherry picked from commit a17e5b27c03230cc65ebedc6dc28dbfce5181c79)
Signed-off-by: Aurelien DARRAGON <adarragon@haproxy.com>
(cherry picked from commit c76eff8ecd4853960e57f081fcfddbd87b8d666d)
Signed-off-by: Aurelien DARRAGON <adarragon@haproxy.com>