Spring Boot Autoconfiguration doesn't require temporal-testing module to be in classpath anymore

[Spikhalskiy]

Bring a level of indirection to don't require test framework classes to be in classpath for non-test functionality

Solves

Caused by: java.lang.IllegalStateException: Failed to introspect Class [io.temporal.spring.boot.autoconfigure.ServiceStubsAutoConfiguration] from ClassLoader [jdk.internal.loader.ClassLoaders$AppClassLoader@277050dc]
[12:25](https://temporaltechnologies.slack.com/archives/D029WJKUN15/p1660926322965759)
Caused by: java.lang.NoClassDefFoundError: io/temporal/testing/TestWorkflowEnvironment
	at java.base/java.lang.Class.getDeclaredMethods0(Native Method) ~[na:na]
	at java.base/java.lang.Class.privateGetDeclaredMethods(Class.java:3166) ~[na:na]
	at java.base/java.lang.Class.getDeclaredMethods(Class.java:2309) ~[na:na]
	at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:467) ~[spring-core-5.3.22.jar:5.3.22]

when users don't even configure TestServer to be used.

Towards #8