Docs/add slug documentation

[tania-campos]

What problem is this solving?

Clients are trying to execute the productsByIdentifier query adding slug to the field field, that is not accepted. Impacting on query usage and project implementation time.

How should this be manually tested?

Workspace

Checklist/Reminders

• Updated README.md.
• Updated CHANGELOG.md.
• Linked this PR to a Clubhouse story (if applicable).
• Updated/created tests (important for bug fixes).
• Deleted the workspace after merging this PR (if applicable).

Screenshots or example usage

Type of changes

✔️	Type of Change
_	Bug fix
_	New feature
_	Breaking change
✔️	Technical improvements

Notes

[vtex-io-ci-cd]

Hi! I'm VTEX IO CI/CD Bot and I'll be helping you to publish your app! 🤖

Please select which version do you want to release:

• Patch (backwards-compatible bug fixes)

• Minor (backwards-compatible functionality)

• Major (incompatible API changes)

And then you just need to merge your PR when you are ready! There is no need to create a release commit/tag.

• No thanks, I would rather do it manually 😞

[vtex-io-docs-bot]

Beep boop 🤖

Thank you so much for keeping our documentation up-to-date ❤️