Provide relevant default values for Enums

This commits adds manual metadata for enums that have a default value
since the annotation processor is not able to detect that yet.

Closes gh-7890

spring-boot-actuator/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -199,6 +199,14 @@
     "description": "Enable git info.",
     "defaultValue": true
   },
+  {
+    "name": "management.info.git.mode",
+    "defaultValue": "simple"
+  },
+  {
+    "name": "management.security.sessions",
+    "defaultValue": "stateless"
+  },
   {
     "name": "spring.git.properties",
     "type": "java.lang.String",