Promote plugin dependency management

This commit promotes the plugin dependency management for the
`maven-enforcer-plugin` and `maven-invoker-plugin` to the root. That way
these can be used in samples as well rather than having a separate copy.

Closes gh-7517

spring-boot-dependencies/pom.xml

@@ -2451,6 +2451,11 @@
 					<artifactId>maven-eclipse-plugin</artifactId>
 					<version>2.10</version>
 				</plugin>
+				<plugin>
+					<groupId>org.apache.maven.plugins</groupId>
+					<artifactId>maven-enforcer-plugin</artifactId>
+					<version>1.4</version>
+				</plugin>
 				<plugin>
 					<groupId>org.apache.maven.plugins</groupId>
 					<artifactId>maven-failsafe-plugin</artifactId>
@@ -2461,6 +2466,11 @@
 					<artifactId>maven-install-plugin</artifactId>
 					<version>2.5.2</version>
 				</plugin>
+				<plugin>
+					<groupId>org.apache.maven.plugins</groupId>
+					<artifactId>maven-invoker-plugin</artifactId>
+					<version>1.10</version>
+				</plugin>
 				<plugin>
 					<groupId>org.apache.maven.plugins</groupId>
 					<artifactId>maven-help-plugin</artifactId>

spring-boot-parent/pom.xml

@@ -293,16 +293,6 @@
 						</dependency>
 					</dependencies>
 				</plugin>
-				<plugin>
-					<groupId>org.apache.maven.plugins</groupId>
-					<artifactId>maven-invoker-plugin</artifactId>
-					<version>1.10</version>
-				</plugin>
-				<plugin>
-					<groupId>org.apache.maven.plugins</groupId>
-					<artifactId>maven-enforcer-plugin</artifactId>
-					<version>1.4</version>
-				</plugin>
 				<plugin>
 					<groupId>org.apache.maven.plugins</groupId>
 					<artifactId>maven-failsafe-plugin</artifactId>

spring-boot-samples/pom.xml

@@ -153,7 +153,6 @@
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-enforcer-plugin</artifactId>
-				<version>1.4</version>
 				<executions>
 					<execution>
 						<id>enforce-rules</id>

spring-boot-samples/spring-boot-sample-custom-layout/pom.xml

@@ -41,7 +41,6 @@
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-invoker-plugin</artifactId>
-				<version>1.10</version>
 				<configuration>
 					<cloneProjectsTo>${project.build.directory}/it</cloneProjectsTo>
 					<settingsFile>src/it/settings.xml</settingsFile>