Add an error message to better explain Java 11+ build requirement (#2081)

* Add an error message to better explain Java 11+ build requirement

* Better wording

* Merge

build.gradle

@@ -10,6 +10,13 @@ plugins {
     id "io.morethan.jmhreport" apply false
 }
 
+if (!JavaVersion.current().isJava11Compatible()) {
+    throw new GradleException("JDK 11 or higher is required to build. " +
+            "One option is to download it from https://adoptopenjdk.net/. If you believe you already " +
+            "have it, please check that the JAVA_HOME environment variable is pointing at the " +
+            "JDK 11 installation.")
+}
+
 ext {
     opentelemetryProjects = subprojects - project(":opentelemetry-bom")
 }