Add shortcut for build config

cf.

* https://github.com/spring-projects/spring-boot/blob/v1.5.1.RELEASE/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jdbc/DataSourceProperties.java#L181
* https://github.com/spring-projects/spring-boot/blob/v1.5.1.RELEASE/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jdbc/DataSourceBuilder.java#L68

Author: backpaper0

doma-spring-boot-autoconfigure/src/main/java/org/seasar/doma/boot/autoconfigure/DomaConfigBuilder.java

@@ -178,4 +178,8 @@ public DomaConfigBuilder entityListenerProvider(
 		this.entityListenerProvider = entityListenerProvider;
 		return this;
 	}
+
+	public DomaConfig build() {
+	    return new DomaConfig(this);
+	}
 }

doma-spring-boot-autoconfigure/src/main/java/org/seasar/doma/boot/autoconfigure/DomaProperties.java

@@ -88,6 +88,13 @@ public void setExceptionTranslationEnabled(boolean exceptionTranslationEnabled)
 		this.exceptionTranslationEnabled = exceptionTranslationEnabled;
 	}
 
+    public DomaConfigBuilder initializeDomaConfigBuilder() {
+        return new DomaConfigBuilder()
+                .dialect(dialect.create())
+                .sqlFileRepository(sqlFileRepository.create())
+                .naming(naming.naming());
+    }
+
 	public static enum DialectType {
 		STANDARD(StandardDialect::new), SQLITE(SqliteDialect::new), DB2(Db2Dialect::new), MSSQL(
 				MssqlDialect::new), MSSQL2008(Mssql2008Dialect::new), MYSQL(