Add Jenkins file to replace github actions

Jenkinsfile

+
+pipeline {
+ 
+  agent {
+    kubernetes {
+      label 'hugo-agent'
+      yaml """
+apiVersion: v1
+metadata:
+  labels:
+    run: hugo
+  name: hugo-pod
+spec:
+  containers:
+    - name: jnlp
+      volumeMounts:
+      - mountPath: /home/jenkins/.ssh
+        name: volume-known-hosts
+      env:
+      - name: "HOME"
+        value: "/home/jenkins"
+    - name: hugo
+      image: eclipsecbi/hugo:0.81.0
+      command:
+      - cat
+      tty: true
+  volumes:
+  - configMap:
+      name: known-hosts
+    name: volume-known-hosts
+"""
+    }
+  }
+ 
+  triggers { pollSCM('H/10 * * * *') 
+ }
+ 
+  options {
+    buildDiscarder(logRotator(numToKeepStr: '5'))
+    checkoutToSubdirectory('hugo')
+  }
+ 
+  stages {
+    stage('Build website (main) with Hugo') {
+      when {
+        branch 'main'
+      }
+      steps {
+        container('hugo') {
+            dir('hugo') {
+                sh 'yarn install --frozen-lockfile && hugo --gc --minify --buildFuture'
+            }
+        }
+      }
+    }
+  }
+}