feat: add GenerateGraphiQLHeaders as new param in createGraphQLHandler

[alicelovescake]

Draft PR

• Fixes RFC: Improve GraphQL DX by setting authentication headers in GraphiQL #5007

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[dthyresson]

I also noticed this issue which could be related?

dotansimha/graphql-yoga#1163

[dthyresson]

We'll pair soon to go over how we might mock the credentials per auth provider

[dthyresson]

@alicelovescake I tried to resolve conflicts and gets tests to pass. Can your review so we can merge?

Note: I had to add a null check the in the shared code for dbAuth when checking cookies.

[alicelovescake]

@dthyresson Good catch on the checking for null case when checking the session cookie. I just changed the cookie from graphiql header to return undefined so we don't have to do the extra null check. Otherwise, I think we are good to merge

const cookieFromGraphiqlHeader =
    process.env.NODE_ENV === 'development'
      ? JSON.parse(event.body ?? '{}').extensions.headers.cookie
      : undefined

[alicelovescake]

@dthyresson made some minor fixes to get the tests passing. I don't have write access so if you think it looks good, you can merge!