feat(admin): export tool for full migration / backup (#5294)

* feat: export content utility (wip)

* feat: export navigation + groups + users

* feat: export comments + navigation + pages + pages history + settings

* feat: export assets

server/core/scheduler.js

@@ -60,7 +60,7 @@ class Job {
           cwd: WIKI.ROOTPATH,
           stdio: ['inherit', 'inherit', 'pipe', 'ipc']
         })
-        const stderr = [];
+        const stderr = []
         proc.stderr.on('data', chunk => stderr.push(chunk))
         this.finished = new Promise((resolve, reject) => {
           proc.on('exit', (code, signal) => {