Basic ability to choose a file for a linksTo(FileDef) field#3876

lukemelia wants to merge 3 commits intomaincardstack/boxel:mainfrom

cs-8391-deal-with-new-case-upload-ui-needs-to-plugin-where-cardcardstack/boxel:cs-8391-deal-with-new-case-upload-ui-needs-to-plugin-where-cardCopy head branch name to clipboard