BUG/MEDIUM: proto_htx: Don't add EOM on 1xx informational messages

BUG/MEDIUM: proto_htx: Don't add EOM on 1xx informational messages

Since the commit b75b5eaf ("MEDIUM: htx: 1xx messages are now part of the final
reponses"), these messages are part of the response and should not contain
EOM. This block is skipped during responses parsing, but analyzers still add it
for "100-Continue" and "103-Eraly-Hints". It can also be added for error files
with 1xx status code.

Now, when HAProxy generate such transitional responses, it does not emit EOM
blocks. And informational messages are now forbidden in error files.

This patch must be backported to 2.0.