Resolves WEB-99:
- pins quicksearch gem to commit for rails 6.1 upgrade two years ago (there've been some breaking updates since then)
- upgraded dul_quicksearch app to use Ruby 3.1.4
- added a snippet in dul_quicksearch initializer to deal with breaking changes introduced with Psych 4.0 via Ruby 3.1 (re: safe loading yml)