Disable CLA Assistant locking PR's

[larcher]

CLA Assistant has a feature to lock a PR after merge. We want this disabled.
Also moving signature to a separate branch for now.

[github-actions]

CLA Assistant Lite bot:
Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request}