[Build] Provide credentials for Git LFS fetch or suppress LFS fetch

Fetching Large File Storage (LFS) objects from GitHub seems to require
authentication now, even when cloning via https.

For the RelEng jobs that are cloning submodules, checking out and
fetching LFS objects is actually not necessary to fulfill their tasks
and therefore just suppressed.

Fixes #3329

Author: HannesWell

JenkinsJobs/Builds/build.jenkinsfile

@@ -131,6 +131,7 @@ spec:
 	  stage('Clone Repositories'){
           steps {
 				dir("${CJE_ROOT}/mbscripts") {
+					withCredentials([gitUsernamePassword(credentialsId: 'github-bot')]) {
                   sshagent(['github-bot-ssh']) {
                     sh '''
                         set -eo pipefail
@@ -139,6 +140,7 @@ spec:
                         ./mb100_cloneRepos.sh $CJE_ROOT/buildproperties.shsource 2>&1 | tee $logDir/mb100_cloneRepos.sh.log
                     '''
                   }
+					}
 				}
 			}
 		}

JenkinsJobs/Releng/prepareNextDevCycle.jenkinsfile

@@ -83,6 +83,9 @@ pipeline {
 			}
 		}
 		stage('Checkout SCM') {
+			environment {
+				GIT_LFS_SKIP_SMUDGE = '1' // Disable unncessary git-lfs fetch (which also requires credentials)
+			}
 			steps {
 				checkout scm
 				script { // Always load the script from the very same state this pipeline is loaded (to ensure consistency)

JenkinsJobs/Releng/promoteBuild.jenkinsfile

@@ -83,6 +83,9 @@ pipeline {
 			}
 		}
 		stage('Checkout SCM') {
+			environment {
+				GIT_LFS_SKIP_SMUDGE = '1' // Disable unncessary git-lfs fetch (which also requires credentials)
+			}
 			steps {
 				dir("${WORKSPACE}/repository") {
 					checkout scm