Add gtcETH to CowSwap.json

[Mr-Madila]

No description provided.

[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}

[alfetopito]

Hi @Mr-Madila thank you for your contribution.

I've recreated the PR optimizing the image #45

We'll soon have the whole process automated which will make this simpler :)