update: up the limit on form data size for HTTP requests

• update: up the limit on form data size for HTTP requests

hCaptcha challenge data exceeded default max size, so a bump was needed. Upped to 8KB to give us space so this doesn't happen again.

requested review from @malowe

@cguindon permanent fix for eclipsefdn/helpdesk#5508 (closed). 8KB is still probably overkill, but I'd rather slight overkill than to have it happen again for a t1 service.

mentioned in commit 56619cbd

merged