make gitea/Jenkinsfile declarative

dockerfiles/services/gitea/Jenkinsfile

@@ -1,4 +1,7 @@
 pipeline {
+    def workdir = 'dockerfiles/services/gitea'
+    def docker_host = 'dkhost:2376'
+
     agent { label 'docker' }
     options {
         buildDiscarder(logRotator(numToKeepStr: '2'))
@@ -6,6 +9,7 @@ pipeline {
     triggers {
         cron('@weekly')
     }
+
     stages {
         stage('prepare') {
             steps {