Bug 1829618 - Enable Prettier on json files (automatic fixes). r=perftest-reviewers,webcompat-reviewers,extension-reviewers,andi,desktop-theme-reviewers,pip-reviewers,devtools-reviewers,sync-reviewers,mossop,denschub,dao,sparky,robwu,geckoview-reviewers,owlish

Differential Revision: https://phabricator.services.mozilla.com/D176336