Merge branch 'bwill/add-jobs.batch-troubleshooting-docs' into 'master'

Add troubleshooting docs for when a job already exists

See merge request !90906

doc/user/clusters/agent/troubleshooting.md

@@ -207,3 +207,25 @@ to the Helm command when [installing the agent](install/#install-the-agent-in-th
 ```shell 
 kubectl create serviceaccount gitlab-agent -n gitlab-agent
 ```
+
+## Failed to perform vulnerability scan on workload: jobs.batch already exists
+
+```json
+{
+  "level": "error",
+  "time": "2022-06-22T21:03:04.769Z",
+  "msg": "Failed to perform vulnerability scan on workload",
+  "mod_name": "starboard_vulnerability",
+  "error": "running scan job: creating job: jobs.batch \"scan-vulnerabilityreport-b8d497769\" already exists"
+}
+```
+
+The GitLab agent performs vulnerability scans by creating a job to scan each workload. If a scan
+is interrupted, these jobs may be left behind and will need to be cleaned up before more jobs can
+be run. You can clean up these jobs by running:
+
+```shell
+kubectl delete jobs -l app.kubernetes.io/managed-by=starboard -n gitlab-agent
+```
+
+[We're working on making the cleanup of these jobs more robust.](https://gitlab.com/gitlab-org/gitlab/-/issues/362016)