ci: use APM pipeline library (#15636)

it uses APM pipeline library configured in the instance

Jenkinsfile

@@ -1,11 +1,6 @@
 #!/usr/bin/env groovy
 
-library identifier: 'apm@master',
-retriever: modernSCM(
-  [$class: 'GitSCMSource',
-  credentialsId: 'f94e9298-83ae-417e-ba91-85c279771570',
-  id: '37cf2c00-2cc7-482e-8c62-7bbffef475e2',
-  remote: '[email protected]:elastic/apm-pipeline-library.git'])
+@Library('apm@current') _
 
 pipeline {
   agent { label 'ubuntu && immutable' }
@@ -36,12 +31,7 @@ pipeline {
     stage('Checkout') {
       options { skipDefaultCheckout() }
       steps {
-        //TODO we need to configure the library in Jenkins to use privileged methods.
-        //gitCheckout(basedir: "${BASE_DIR}")
-        dir("${BASE_DIR}"){
-          checkout scm
-          githubEnv()
-        }
+        gitCheckout(basedir: "${BASE_DIR}")
         stash allowEmpty: true, name: 'source', useDefaultExcludes: false
         script {
           env.GO_VERSION = readFile("${BASE_DIR}/.go-version").trim()