fix includeUnusedVariables not working with BatchHttpLink

[sincraianul]

Checklist:

• If this PR contains changes to the library itself (not necessary for e.g. docs updates), please include a changeset (see CONTRIBUTING.md)
• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests

[apollo-cla]

@sincraianul: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Apollo Contributor License Agreement here: https://contribute.apollographql.com/

[netlify]

‼️ Deploy request for apollo-client-docs rejected.

Name	Link
🔨 Latest commit	5e4c894

[changeset-bot]

🦋 Changeset detected

Latest commit: b301242

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@apollo/client	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[osdiab]

this closes #8824

[sincraianul]

@benjamn @alessbell @bignimbus @hwillson @jerelmiller @phryneas Would be awesome to get a release for this ASAP as it's something critical to our use case. Thanks!

[alessbell]

Hi @sincraianul 👋

Thanks for taking the time to look into this and opening a PR!

While an argument can be made for targeting this at a patch release (since the BatchHttpLink has long included includeUnusedVariables in its options type), since this will add functionality and do a light refactor re: extracting filterOperationVariables (and since we're in the home stretch before releasing the next minor, 3.8 🎉) we'd like to target this at the release-3.8 branch.

I'll make that change and we'll get this reviewed as soon as we can. Thanks!

[jerelmiller]

Thanks so much for fixing this @sincraianul 🔥 🔥. We will make sure this goes out with the next v3.8.0-alpha.x release!