Update to Spring Boot 2.4.0

Closes gh-9248

Author: jzheaux

gradle.properties

@@ -1,7 +1,7 @@
 aspectjVersion=1.9.6
 gaeVersion=1.9.82
 springJavaformatVersion=0.0.25
-springBootVersion=2.4.0-M3
+springBootVersion=2.4.0
 version=5.4.2-SNAPSHOT
 kotlinVersion=1.4.10
 org.gradle.jvmargs=-Xmx3g -XX:MaxPermSize=2048m -XX:+HeapDumpOnOutOfMemoryError