Update to Spring Boot 2.7.0

Closes gh-749

samples/custom-consent-authorizationserver/samples-custom-consent-authorizationserver.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id "org.springframework.boot" version "2.6.7"
+	id "org.springframework.boot" version "2.7.0"
 	id "io.spring.dependency-management" version "1.0.11.RELEASE"
 	id "java"
 }

samples/default-authorizationserver/samples-default-authorizationserver.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id "org.springframework.boot" version "2.6.7"
+	id "org.springframework.boot" version "2.7.0"
 	id "io.spring.dependency-management" version "1.0.11.RELEASE"
 	id "java"
 }

samples/federated-identity-authorizationserver/samples-federated-identity-authorizationserver.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id "org.springframework.boot" version "2.6.7"
+	id "org.springframework.boot" version "2.7.0"
 	id "io.spring.dependency-management" version "1.0.11.RELEASE"
 	id "java"
 }

samples/messages-client/samples-messages-client.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id "org.springframework.boot" version "2.6.7"
+	id "org.springframework.boot" version "2.7.0"
 	id "io.spring.dependency-management" version "1.0.11.RELEASE"
 	id "java"
 }

samples/messages-resource/samples-messages-resource.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id "org.springframework.boot" version "2.6.7"
+	id "org.springframework.boot" version "2.7.0"
 	id "io.spring.dependency-management" version "1.0.11.RELEASE"
 	id "java"
 }