BUG/MEDIUM: h3: reject request with invalid pseudo header

BUG/MEDIUM: h3: reject request with invalid pseudo header

RFC 9114 dictates several requirements for pseudo header usage in H3
request. Previously only minimal checks were implemented. Enforce all
the following requirements with this patch :
* reject request with undefined or invalid pseudo header
* reject request with duplicated pseudo header
* reject non-CONNECT request with missing mandatory pseudo header
* reject request with pseudo header after standard ones

For the moment, this kind of errors triggers a connection close. In the
future, it should be handled only with a stream reset. To reduce
backport surface, this will be implemented in another commit.

This must be backported up to 2.6.