nit: add rate limit extension example

[sbilello]

Add Rate Limit Extension Example

[linux-foundation-easycla]

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• ✅ login: sbilello / name: Sergio Bilello (3fba591)

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[benjie]

Generally it's good practice to namespace the top fields in extensions to avoid conflicts, since the meaning is effectively granted to them by the entire ecosystem as a whole with no real governing documents/registry. For example, this rateLimit might be confused by some tooling with a different rateLimit format and result in errors. Instead: sb_rateLimit would be safer, or even extensions:{sb:{rateLimit:{...}}}.

Out of interest, what motivated this addition in particular?

[sbilello]

@benjie I've revised the example to better demonstrate how developers can implement rate-limiting using the extensions. Could you take a look please?
Thanks

[benjie]

This wasn't valid JSON since it had {{ ... }}

Suggested change

	{
	"customNamespace" : {
	"requestRate": 2,
	"remaining": 98,
	"retryAfterMs": 0,
	"resetAfterMs": 1985
	}
	}
	"customNamespace": {
	"requestRate": 2,
	"remaining": 98,
	"retryAfterMs": 0,
	"resetAfterMs": 1985
	}

[sbilello]

fixed

[benjie]

I'm not convinced that the GraphQL spec needs an example of using the extensions property. I'll leave this open in case others feel otherwise.

[sbilello]

Thanks, @benjie! I fixed the json validation.
I wanted to add an example to make sure that developers are aware about the difference between extensions for errors and extensions for not errors