This PR includes changes:
1. Rename `type` field to `thresholdType` (enum 'above' or 'below')
2. Introduce alert source enum ('saved_search' or 'tile')
3. Rename `dashboardId` field to `dashboard`
4. Deprecate unused `cron` field
5. Deprecate external alert translation layers
6. Deprecate `appType` flag
7. Copied over 'common' pkgs from app dir (mostly clickhouse query helpers + types) -> will become a sharable pkg between app and api
