Add settings.yml

[Pandapip1]

Blockers: #5418, #5400, an admin of @ethereum installing https://github.com/apps/settings for this repository

Closes #5414

[eth-bot]

Hi! I'm a bot, and I wanted to automerge your PR, but couldn't because of the following issue(s):

---

(fail) .github/CODEOWNERS

classification
ambiguous

• '.github/CODEOWNERS' must be in eip-###.md format; this error will be overwritten upon relevant editor approval

(fail) .github/settings.yml

classification
ambiguous

• '.github/settings.yml' must be in eip-###.md format; this error will be overwritten upon relevant editor approval

[lightclient]

I prefer to not use settings.yml. We have had some problems with branch protection in the past and I am not comfortable with someone potentially getting a malicious commit into it.

[Pandapip1]

I'll close this for now, until everything has been settled.