Add `includeUnusedVariables` option support

[storm2513]

Issue description

This option is present in createHttpLink, but missing in createUploadLink

Reason why this option was added is explained here: https://github.com/apollographql/apollo-client/pull/7127

What changes have been made?

• added includeUnusedVariables option support (same approach as in apollo-client repo)
• added tests