MEDIUM: http-rules: Make early-hint custom actions

MEDIUM: http-rules: Make early-hint custom actions

Now, the early-hint action uses its own dedicated action and is no longer
handled "in place" during the HTTP rules evaluation. Thus the action name
ACT_HTTP_EARLY_HINT is removed. In additionn, http_add_early_hint_header() and
http_reply_103_early_hints() are also removed. This part is now handled in the
new action_ptr callback function.