security: Update to Spring Boot 2.6.6 to address CVE-2022-22965 (#366)

https://snyk.io/blog/spring4shell-zero-day-rce-spring-framework-explained/
Updating to Spring Boot 2.6.6 remediates the CVE

Author: jeffhubLR

pom.xml

@@ -6,7 +6,7 @@
     <parent>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-parent</artifactId>
-        <version>2.6.3</version>
+        <version>2.6.6</version>
     </parent>
     <groupId>com.obsidiandynamics.kafdrop</groupId>
     <artifactId>kafdrop</artifactId>