defer integration tests

[Geal]

This adds support for testing @defer in integration tests

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Checklist

Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.

• Changes are compatible¹
• Documentation² completed
• Performance impact assessed and acceptable
• Tests added and passing³
  • Unit Tests
  • Integration Tests
  • Manual Tests

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Notes

Footnotes

1. It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this. ↩

2. Configuration is an important part of many changes. Where applicable please try to document configuration examples. ↩

3. Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions. ↩

[github-actions]

@Geal, please consider creating a changeset entry in /.changesets/. These instructions describe the process and tooling.

[Geal]

@BrynCooke do you remember why the integration tests were removing the Accept header from the request?

[Geal]

interestingly, multer is unable to parse the multipart body we send with defer and subs:

--graphql
content-type: application/json

{"data":null,"errors":[{"message":"HTTP fetch failed from 'accounts': 404: Not Found","path":[],"extensions":{"code":"SUBREQUEST_HTTP_ERROR","service":"accounts","reason":"404: Not Found","http":{"status":404}}},{"message":"HTTP fetch failed from 'accounts': subgraph response does not contain 'content-type' header; expected content-type: application/json or content-type: application/graphql-response+json","path":[],"extensions":{"code":"SUBREQUEST_HTTP_ERROR","service":"accounts","reason":"subgraph response does not contain 'content-type' header; expected content-type: application/json or content-type: application/graphql-response+json","http":{"status":404}}}],"hasNext":true}
--graphql
content-type: application/json

{"hasNext":false}
--graphql--

it fails with the error incomplete multipart stream. Maybe some different assumptions in how we chunk the response?

[Geal]

the multer failure was due to a boundary reported as a quoted string

[Geal]

Supporting subscriptions in those tests would be challenging, as they are not designed to execute tasks asynchronously, so we cannot(for now) use the HTTP callback while we are already waiting for a response. We could have subgraph emulation support websockets though