Fail vs. fatal on store startup (#24170)

If the store fails to initialize (e.g. run a migration), it would `log.Fatal` and then `os.Exit`. Unfortunately, this trips up `TestMain`, which happily keeps running tests, now guaranteed to fail.

Avoid this by instead returning an error from the store initialization, handling appropriately at the layer above.

server/channels/app/platform/service.go

@@ -204,7 +204,11 @@ func New(sc ServiceConfig, options ...Option) (*PlatformService, error) {
 			// Timer layer
 			// |
 			// Cache layer
-			ps.sqlStore = sqlstore.New(ps.Config().SqlSettings, ps.metricsIFace)
+			var err error
+			ps.sqlStore, err = sqlstore.New(ps.Config().SqlSettings, ps.metricsIFace)
+			if err != nil {
+				return nil, err
+			}
 
 			searchStore := searchlayer.NewSearchLayer(
 				retrylayer.New(ps.sqlStore),