MINOR: http: support default hardening names "untrusted" and "trusted"

MINOR: http: support default hardening names "untrusted" and "trusted"

And also reserve "auto" for future use. Both "untrusted" and "trusted"
have a global storage and are available all the time. They're just not
registered in the tree by default so that we'll find them once missed
in the tree lookup. If a section with these names is created, it
inherits their settings. This will allow new default settings to
change over time, with minimal maintenance effort for the users.

They are preset to the default permissive rules.