Backend for DB sync progress UX (#18952)

resources/migrations/000_migrations.yaml

src/metabase/api/activity.clj

src/metabase/api/database.clj

src/metabase/api/search.clj

src/metabase/api/setup.clj

src/metabase/models/database.clj

src/metabase/models/table.clj

src/metabase/public_settings.clj

src/metabase/search/config.clj

src/metabase/sync/sync_metadata.clj

src/metabase/sync/sync_metadata/fks.clj

src/metabase/sync/util.clj

test/metabase/api/activity_test.clj

test/metabase/api/database_test.clj

test/metabase/api/field_test.clj

test/metabase/api/search_test.clj

test/metabase/api/table_test.clj

test/metabase/sync/util_test.clj

test/metabase/sync_test.clj