Add hashKeyName option for createPersistedQueryLink

[infiniteluke]

Hello! Thanks so much for building such a great library!

apollo-link-persisted-queries assumes your hash will be sha256, but provides generateHash function to override that which we assumed we’d use to pass our query names. However, It seems strange to send a string like page.v1 as the hash when it is not sha256.

Does that mean I’m using persisted queries in a way they’re not meant to be used or would you accept a PR that allows createPersistedQueryLink to take a hashKeyName to name that key differently?

[apollo-cla]

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

[infiniteluke]

Agreement signed ✅ Build is failing due to being .04KB above the limit 😉