fix "response-padding" configuration and remove optionmaps

fix "response-padding" configuration and remove optionmaps

Add a default "response-padding" option in the global defaults,
to disable the option, and simplify the configuration code so that
looks at the global defaults if the option is not set in named.conf.

This enables us to remove the 'optionmaps' variable in configure_view(),
which was used for options that only look in named.conf.

(cherry picked from commit cf409e814f13c932d92fae5d85ddd16ac7ebfdc0)