Add static variable for metadata table string path

[spring0913]

Issue #4586

Motivation

@Bean
public DataSource dataSource() {
    return new EmbeddedDatabaseBuilder()
		.addScript("/org/springframework/batch/core/schema-h2.sql")
		.build();
}

• On Add static variables to prevent typos in the metadata tables string path #4586, I think it is better to use static variables to prevent typos in the metadata table creation script path string.

Modification

@Bean
public DataSource dataSource() {
    return new EmbeddedDatabaseBuilder()
		.addScript(DatabaseResource.SCHEMA_H2)
		.build();
}

• Add static variable for metadata table string path.