Remove the unconditional exposure of the transaction manager as a bean

This commit removes the unconditional exposure of the transaction
manager as a bean in the application context. The transaction manager
is still taken from the BatchConfigurer and set where needed (ie on
JobRepository and StepBuilderFactory) as previously done,
but is not exposed anymore as a bean to prevent any clash with a user
defined transaction manager.

If no transaction manager is provided, a DataSourceTransactionManager
will be configured by default as required by batch (without being exposed
as a bean).

Resolves #816

spring-batch-samples/src/main/java/org/springframework/batch/sample/remotechunking/DataSourceConfiguration.java

@@ -20,6 +20,7 @@ import javax.sql.DataSource;
 
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.jdbc.datasource.DataSourceTransactionManager;
 import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseBuilder;
 
 /**
@@ -37,4 +38,9 @@ public class DataSourceConfiguration {
 				.build();
 	}
 
+	@Bean
+	public DataSourceTransactionManager transactionManager(DataSource dataSource) {
+		return new DataSourceTransactionManager(dataSource);
+	}
+
 }

spring-batch-samples/src/main/java/org/springframework/batch/sample/remotepartitioning/DataSourceConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018 the original author or authors.
+ * Copyright 2018-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,7 @@ import org.springframework.beans.factory.annotation.Value;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.PropertySource;
+import org.springframework.jdbc.datasource.DataSourceTransactionManager;
 
 /**
  * @author Mahmoud Ben Hassine
@@ -50,4 +51,9 @@ public class DataSourceConfiguration {
 		return dataSource;
 	}
 
+	@Bean
+	public DataSourceTransactionManager transactionManager(DataSource dataSource) {
+		return new DataSourceTransactionManager(dataSource);
+	}
+
 }