Warn Java 11 users of 18 Jun 2024 end of life in weekly (jenkinsci#9314)

Alert Java 11 users of 18 Jun 2024 end of life in weekly

Also updates the Java 11 end of life date for Java 11 users running with
the long term support release.

core/src/main/java/jenkins/monitor/JavaVersionRecommendationAdminMonitor.java

@@ -78,7 +78,16 @@ public class JavaVersionRecommendationAdminMonitor extends AdministrativeMonitor
 
     static {
         NavigableMap<Integer, LocalDate> supportedVersions = new TreeMap<>();
-        supportedVersions.put(11, LocalDate.of(2024, 9, 30)); // Temurin: 2024-10-31
+        // Adjust Java 11 end of life date for weekly and LTS
+        if (Jenkins.VERSION.split("[.]").length > 2) {
+            // LTS will require Java 17 or newer beginning 30 Oct 2024
+            // https://groups.google.com/g/jenkinsci-dev/c/gsXAqOQQEPc/m/VT9IBYdmAQAJ
+            supportedVersions.put(11, LocalDate.of(2024, 10, 30)); // Temurin: 2024-10-31
+        } else {
+            // Weekly will require Java 17 or newer beginning 18 Jun 2024
+            // https://groups.google.com/g/jenkinsci-dev/c/gsXAqOQQEPc/m/4fn4Un1iAwAJ
+            supportedVersions.put(11, LocalDate.of(2024, 6, 18)); // Temurin: 2024-10-31
+        }
         supportedVersions.put(17, LocalDate.of(2026, 3, 31)); // Temurin: 2027-10-31
         supportedVersions.put(21, LocalDate.of(2027, 9, 30)); // Temurin: 2029-09-30
         SUPPORTED_JAVA_VERSIONS = Collections.unmodifiableNavigableMap(supportedVersions);