(TK-83) Add :enable-trailing-slash-redirect option

Add new :enable-trailing-slash-redirect option to the options map
for all service functions that add handlers. When true, all
requests made to the handler without a trailing slash will be
redirected to have a trailing slash. Defaults to false.
Not 100% sure how I feel about the option name, but I'm not coming up with anything that is obviously a ton better.  Maybe `redirect-if-no-trailing-slash`?  Or... `redirect-on-null-path`?  Anyone else have any suggestions?