Add Central Portal Snapshots repository for rundeck-core:6.0.0-SNAPSHOT

- OSSRH sunset on June 30, 2025, migrated to Central Portal
- New snapshots URL: https://central.sonatype.com/repository/maven-snapshots/
- Added includeModule() to only search this repo for org.rundeck:rundeck-core
- Tested locally: BUILD SUCCESSFUL
- Reference: https://central.sonatype.org/publish/publish-portal-upload/#consuming--snapshot-releases-for-your-project

Author: fdevans

build.gradle

@@ -38,9 +38,12 @@ defaultTasks 'clean','build'
 repositories {
     mavenLocal()
     maven {
-        url "https://oss.sonatype.org/content/repositories/snapshots/"
-        mavenContent {
-            snapshotsOnly()
+        name = 'Central Portal Snapshots'
+        url = 'https://central.sonatype.com/repository/maven-snapshots/'
+        
+        // Only search this repository for rundeck-core snapshots
+        content {
+            includeModule('org.rundeck', 'rundeck-core')
         }
     }
     mavenCentral()