Fix custom workflow on CentOS

On CentOS distros the custom workflow authentication token is now written to /dev/kmsg. This results in a time stamp written before the JSON.

Solution: Strip anything before the first curly brace, just like we do when parsing the console log for server resource usage.

Background, see commit: 030aceb8

How to Test

For each of the images: CentOS 8, Ubuntu 20, AlmaLinux, and Rocky:

• Launch instances including a custom workflow, e.g. https://github.com/binder-examples/minimal-dockerfile
• Ensure that the Workflow interaction button becomes active (green)
• Ensure that when you press on the Workflow interaction button that you see the Jupyter environment

Screenshots

No visual changes

QA Checklist

• Any changes to 'widgets' in src/Style/Widgets/? If so:
  • Update src/Style/StyleGuide.elm showing example usage of that widget
• Were any app flags created, modified, or removed? If so:
  • Update config.js and all files in environment-configs/, including docker-config.js
  • Update "Runtime configuration options" documentation in README.md

Post-Merge Checklist

• Create follow-up issues for anything left over for another merge request
  • If any technical debt is introduced, assign these follow-up issues to the MR submitter