Initial support for SB3/SF6

- Main branch builds successfully (with tests skipped)

See #326

functions/function/header-enricher-function/src/main/java/org/springframework/cloud/fn/header/enricher/HeaderEnricherFunctionProperties.java

@@ -18,7 +18,7 @@ package org.springframework.cloud.fn.header.enricher;
 
 import java.util.Properties;
 
-import javax.validation.constraints.NotNull;
+import jakarta.validation.constraints.NotNull;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.validation.annotation.Validated;