Conditional for Spanner is based on missing beans of type SpannerTransactionManager instead of PlatformTransactionManager, this way it always gets created if Spanner libs are pulled in
Conditional for Datastore is based on missing beans of type DatastoreTransactionManager instead of PlatformTransactionManager, this way it gets created if Datastore libs are pulled in
It is user responsibility to designate the transaction's right transaction manager:
```
@transactional(transactionManager = "spannerTransactionManager")
```

```
@transactional(transactionManager = "datastoreTransactionManager")
```