Add CSP for form_action and frame_ancestors
Add CSP for form_action and frame_ancestors

We received a report that `X-Frame-Options` can be bypassed if
rubygems.org was behind a proxy.

sonalkr132/rubygems.org,sonalkr132/rubygems.org,sonalkr132/rubygems.org,rubygems/rubygems.org,sonalkr132/rubygems.org,rubygems/rubygems.org,rubygems/rubygems.org,rubygems/rubygems.org