refactor: checkUsernameAvailability to async (#28557)

apps/meteor/app/api/server/v1/users.ts

apps/meteor/app/apps/server/bridges/users.ts

apps/meteor/app/authentication/server/startup/index.js

...eor/app/channel-settings/server/functions/saveRoomName.js

apps/meteor/app/invites/server/functions/useInviteToken.js

...eor/app/lib/server/functions/checkUsernameAvailability.ts

apps/meteor/app/lib/server/functions/createRoom.ts

apps/meteor/app/lib/server/functions/index.ts

apps/meteor/app/lib/server/functions/saveUser.js

apps/meteor/app/lib/server/functions/setUsername.ts

...eteor/app/lib/server/methods/checkUsernameAvailability.ts

apps/meteor/app/lib/server/methods/setUsername.ts

apps/meteor/app/livechat/imports/server/rest/users.ts

apps/meteor/app/livechat/server/lib/Livechat.js

...d-responses/server/hooks/onMessageSentParsePlaceholder.ts

.../app/livechat-enterprise/server/lib/LivechatEnterprise.js

apps/meteor/server/lib/roles/addUserRoles.ts

apps/meteor/server/lib/spotlight.js

apps/meteor/server/publications/spotlight.ts

apps/meteor/server/services/team/service.ts