Document how to re-enable DataSource auto-config when using R2DBC

Closes gh-22094

spring-boot-project/spring-boot-docs/src/docs/asciidoc/spring-boot-features.adoc

@@ -4055,7 +4055,8 @@ The following examples shows how to set some PostgreSQL connection options:
 	}
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-When a `ConnectionFactory` bean is available, the regular jdbc `DataSource` auto-configuration backs off.
+When a `ConnectionFactory` bean is available, the regular JDBC `DataSource` auto-configuration backs off.
+If you want to retain the JDBC `DataSource` auto-configuration, and are comfortable with the risk of using the blocking JDBC API in a reactive application, add `@Import(DataSourceAutoConfiguration.class)` on a `@Configuration` class in your application to re-enable it.