feat(persisted-fetch): Add enableForMutation option

[geekuillaume]

Resolve #1287

Summary

This PR adds the enableForMutation option to PersistedFetchExchangeOptions to allow running the persisted operations logic on mutation in addition to queries.

Set of changes

• Add enableForMutation option to PersistedFetchExchangeOptions (optional and default false to keep backward compatibility)
• Check enableForMutation option when filtering operations in the exchange

[JoviDeCroock]

A few things that stood out during review, will talk about this with a co-maintainer as we normally start with an RFC before introducing changes like this as detailed in the contributing

We'd also have to send these as POST not as GET to avoid running the risk of caching these which would warrant a change on line 95 to not use get when this is enabled && we are dealing with an operation of kind mutation.

[geekuillaume]

I refactored the part of the code dedicated to filtering in/out the operation as a persisted fetch. This should be clearer and makes sure that the operation is either using the persisted fetch exchange or the next exchange (but never both or 0 of them). I also added a check to prevent GET requests for mutation, only for queries. I added more details about these changes in the documentation

[kitten]

Looks good to me! 👍 Thanks for sending a detailed PR. I just have a small nit to add.
Checks are approved and running now.