Jenkins improvements (#1368)

- Show changes in the Discord webhook
- Delete after 20 builds

Co-authored-by: rtm516 <ryantmilner@hotmail.co.uk>

Jenkinsfile

@@ -5,7 +5,7 @@ pipeline {
         jdk 'Java 8'
     }
     options {
-        buildDiscarder(logRotator(artifactNumToKeepStr: '5'))
+        buildDiscarder(logRotator(artifactNumToKeepStr: '20'))
     }
     stages {
         stage ('Build') {
@@ -32,9 +32,40 @@ pipeline {
 
     post {
         always {
+            script {
+                def changeLogSets = currentBuild.changeSets
+                def message = "**Changes:**"
+
+                if (changeLogSets.size() == 0) {
+                    message += "\n*No changes.*"
+                } else {
+                    def repositoryUrl = scm.userRemoteConfigs[0].url.replace(".git", "")
+                    def count = 0;
+                    def extra = 0;
+                    for (int i = 0; i < changeLogSets.size(); i++) {
+                        def entries = changeLogSets[i].items
+                        for (int j = 0; j < entries.length; j++) {
+                            if (count <= 10) {
+                                def entry = entries[j]
+                                def commitId = entry.commitId.substring(0, 6)
+                                message += "\n   - [`${commitId}`](${repositoryUrl}/commit/${entry.commitId}) ${entry.msg}"
+                                count++
+                            } else {
+                                extra++;
+                            }
+                        }
+                    }
+                    
+                    if (extra != 0) {
+                        message += "\n   - ${extra} more commits"
+                    }
+                }
+
+                env.changes = message
+            }
             deleteDir()
             withCredentials([string(credentialsId: 'geyser-discord-webhook', variable: 'DISCORD_WEBHOOK')]) {
-                discordSend description: "**Build:** [${currentBuild.id}](${env.BUILD_URL})\n**Status:** [${currentBuild.currentResult}](${env.BUILD_URL})\n\n[**Artifacts on Jenkins**](https://ci.nukkitx.com/job/Geyser)", footer: 'NukkitX Jenkins', link: env.BUILD_URL, successful: currentBuild.resultIsBetterOrEqualTo('SUCCESS'), title: "${env.JOB_NAME} #${currentBuild.id}", webhookURL: DISCORD_WEBHOOK
+                discordSend description: "**Build:** [${currentBuild.id}](${env.BUILD_URL})\n**Status:** [${currentBuild.currentResult}](${env.BUILD_URL})\n${changes}\n\n[**Artifacts on Jenkins**](https://ci.nukkitx.com/job/Geyser)", footer: 'Cloudburst Jenkins', link: env.BUILD_URL, successful: currentBuild.resultIsBetterOrEqualTo('SUCCESS'), title: "${env.JOB_NAME} #${currentBuild.id}", webhookURL: DISCORD_WEBHOOK
             }
         }
     }