ci: create version_info.json file

Will be used for exporting version metrics.

Signed-off-by: Jakub Sokołowski <jakub@status.im>

Jenkinsfile

@@ -1,3 +1,5 @@
+import groovy.json.JsonBuilder
+
 pipeline {
   agent { label 'linux' }
 
@@ -45,6 +47,17 @@ pipeline {
   }
 
   stages {
+    stage('Prep') {
+      steps { script {
+        def jobMetaJson = new JsonBuilder([
+          git_commit: env.GIT_COMMIT.take(7),
+          git_branch: env.GIT_BRANCH,
+          build_id:   env.BUILD_ID,
+        ]).toPrettyString()
+        sh "echo '${jobMetaJson}' > version_info.json"
+      } }
+    }
+
     stage('Build') {
       steps { script {
         dir("spiffworkflow-${params.COMPONENT}") {