use body.extensions

[Rowadz]

when sending an extensions object with a get request the package expects an extensions in the query params, but when doing a post request it expects an object called extension in the payload

I believe this is a bug.

graphql-helix/packages/core/lib/get-graphql-parameters.ts

Lines 12 to 21 in f8e9b1a

	if (isHttpMethod("GET", method)) {
	operationName = queryParams.operationName;
	query = queryParams.query;
	variables = queryParams.variables;
	extensions = queryParams.extensions;
	} else if (isHttpMethod("POST", method)) {
	operationName = body?.operationName;
	query = body?.query;
	variables = body?.variables;
	extensions = body?.extension

I opened this PR to fix it ツ