Make ExtensionsTests use TestApplicationBoostrap

- Use TestApplicationBootstrap to get the SingleNodeApplication with
RandomConfigurationSupport
Add explicit health endpoint

- Define @Bean for Health endpoint in ParentConfiguration (XD global beans)
  with @ConditionalOnExpression("${endpoints.health.enabled:true}")
 - Added VanillaHealthIndicator for the health endpoint
instead of the SimpleHealthIndicator which uses dataSource
XD-1437 Exclude slf4j Transitive Dependencies

Force all slf4j dependencies to project version.