Add spring-configuration-metadata

- Adding boot's annotation processor to spring-shell-autoconfigure
  and spring-shell-test-autoconfigure
- Backport #948
- Fixes #950

spring-shell-autoconfigure/spring-shell-autoconfigure.gradle

@@ -11,4 +11,5 @@ dependencies {
 	implementation project(':spring-shell-standard')
 	implementation project(':spring-shell-standard-commands')
 	testImplementation 'org.springframework.boot:spring-boot-starter-test'
+	annotationProcessor 'org.springframework.boot:spring-boot-configuration-processor'
 }