[http] Adapt header field name validation to RFC definition
Merge branch 'hotfix/5318'

Close #5318
Merge pull request #5301 from Maks3w/hotfix/http-fieldname-check

[http] Adapt header field name validation to RFC definition
[#5301] re-add normalization

- s/_/-/ in header field names
Merge branch 'hotfix/5301' into develop

Forward port #5301