Add schema.sql,data.sql to default SQL initializers

...for compatibility with Spring JDBC. Users can still
optionally specify spring.database.schema, but the default
location is schema-${spring.database.platform}.sql, schema.sql,
data.sql.

[Fixes #58332710]

spring-boot-autoconfigure/src/test/resources/schema.sql

@@ -0,0 +1,4 @@
+CREATE TABLE BAR (
+  id         INTEGER IDENTITY PRIMARY KEY,
+  name VARCHAR(30),
+);