BAEL-1314 Guide to AbstractRoutingDatasource (#2989)

* BAEL-1314 initial import.  Guide to AbstractRoutingDatasource.

* BAEL-1314 Guide to Spring AbstractRoutingDatasource

* update test name and rename test classes

* move dsrouting example to spring-boot project.  rename db create script.

spring-boot/src/test/resources/dsrouting-db.sql

@@ -0,0 +1,5 @@
+create table client (
+  id numeric,
+  name  varchar(50),
+  constraint pk_client primary key (id)
+);