use 'plugins' instead of 'apply plugin' in gradle-it

related to quarkusio#1623

just for consistency with the Quick Start and our doc on
https://quarkus.io/guides/gradle-tooling and
https://quarkus.io/guides/gradle-config.html

FTR: This change does not actually fix the currently broken Gradle IT.

devtools/gradle-it/build.gradle

@@ -1,31 +1,11 @@
-apply plugin: 'java'
-apply plugin: 'io.quarkus'
+plugins {
+    id 'java'
+    id 'io.quarkus' version '999-SNAPSHOT'
+}
 
 compileJava.options.encoding = "UTF-8"
 compileTestJava.options.encoding = "UTF-8"
 
-buildscript {
-    repositories {
-        maven { url '../gradle/target/dependencies/' }
-        mavenCentral()
-    }
-    dependencies {
-        classpath fileTree(dir: '../gradle/build/libs', include: 'quarkus-gradle-plugin-*.jar')
-
-        classpath 'io.quarkus:quarkus-bootstrap-core:999-SNAPSHOT'
-        classpath 'io.quarkus:quarkus-devtools-common:999-SNAPSHOT'
-        classpath 'io.quarkus:quarkus-devtools-common-core:999-SNAPSHOT'
-        classpath 'io.quarkus:quarkus-development-mode:999-SNAPSHOT'
-        classpath 'io.quarkus:quarkus-creator:999-SNAPSHOT'
-    }
-}
-
-repositories {
-    //Needs latest from local snapshots too:
-    mavenLocal()
-    mavenCentral()
-}
-
 test {
     useJUnitPlatform()
 }

devtools/gradle-it/settings.gradle

@@ -0,0 +1,15 @@
+pluginManagement {
+    repositories {
+        // TODO ideally this, like build.gradle, should just read from ../gradle instead of mavenLocal(), but it's not clear how
+        // classpath fileTree(dir: '../gradle/build/libs', include: 'quarkus-gradle-plugin-*.jar')
+        // classpath fileTree(dir: '../gradle/target/dependencies/compile', include: '*.jar')
+        mavenLocal()
+    }
+    resolutionStrategy {
+        eachPlugin {
+            if (requested.id.id == 'io.quarkus') {
+                useModule("io.quarkus:quarkus-gradle-plugin:${requested.version}")
+            }
+        }
+    }
+}