[do not review] adding postgres vs dgraph benchmark

[campoy]

This change is 

[CLAassistant]

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.

---

Francesc Campoy seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[github-actions[bot]]

This PR has been stale for 60 days and will be closed automatically in 7 days. Comment to keep it open.