chore(docs): replace non-ASCII quote in kong.conf.default with normal double quote

[hanshuebner]

Summary

The non-ASCII double quote will display as garbage if the locale of the terminal is not correctly set, which is something that can happen with Docker in some cases.

Checklist

• [ ] The Pull Request has tests
• [x] A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• [ ] There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

[bungle]

This must be someone's editor doing "auto-screwup".

[team-gateway-bot]

Successfully created cherry-pick PR for master:

• https://github.com/kong/kong-ee/pull/9603