Restore Format and CheckFormat for saml2 Projects

- Update the way that the saml2 projects were dependent
on identity-provider resource files.
- Use TestContainers to simplify runtime dependencies
- Update compose.yml to use Docker-standard interpolation

Closes gh-335

servlet/spring-boot/java/saml2/refreshable-metadata/settings.gradle

@@ -6,3 +6,6 @@ pluginManagement {
         maven { url "https://repo.spring.io/snapshot" }
     }
 }
+
+include ":servlet:spring-boot:java:saml2:identity-provider"
+project(":servlet:spring-boot:java:saml2:identity-provider").projectDir = file("../identity-provider")