Previously, Quartz could be configured with a specific DataSource
using `@QuartzDataSource` but it was not possible to configure a
Quartz-specific transaction manager. This could result in the
different DataSources being used by Quartz itself and Quart'z
DataSourceTransactionManager.

This commit introduces a new qualifier, `@QuartzTransactionManager`,
that can be used to avoid the above-described problem. Any
`@QuartzTransactionManager`-annotated bean will be used by the
Quartz auto-configure configuration instead of the application's main
`TransactionManager`. If no such qualified bean is present, the
application's main TransactionManager, if any, will be used as before.

Fixes gh-20184