Notification mechanism for realm-core nightly builds (#5661)

nightly.Jenkinsfile

@@ -1 +1,28 @@
-def run = build '/realm/realm-core/master'
+
+import groovy.json.JsonOutput
+def run = build job:'/realm/realm-core/master', propagate: false
+node {
+    withCredentials([[$class: 'StringBinding', credentialsId: 'slack-realm-core-ci-alerts-url', variable: 'SLACK_URL']]) {
+        def payload = null
+        if (run.getResult() == "SUCCESS") {
+            payload = JsonOutput.toJson([
+                    username: "Realm CI",
+                    icon_emoji: ":jenkins:",
+                    text: "*The current realm-core nightly build was ok!*\n<${run.absoluteUrl}|Click here> to check the build."
+            ])
+            currentBuild.result = "SUCCESS"
+        } else if(run.getResult() == "FAILURE"){
+            payload = JsonOutput.toJson([
+                    username: "Realm CI",
+                    icon_emoji: ":jenkins:",
+                    text: "@realm-core-engineers *The current realm-core nightly build is broken!*\n<${run.absoluteUrl}|Click here> to check the build.",
+                    link_names: 1
+            ])
+            currentBuild.result = "FAILURE"
+        }
+        // otherwise the build was aborted, because no nightly build was needed, but in this case we don't need to signal anything
+        if (payload != null) {
+            sh "curl -X POST --data-urlencode \'payload=${payload}\' ${env.SLACK_URL}"
+        }
+    }
+}