Expose sourceHash or id for operations

`fetchQuery`receives `operation.node.params` but it would be nice to have access to `operation.node.hash` to use it for local cache key and mainly for the following approach: first fetch to the server with hash and variables only, if the server contains the hash in its own cache, it directly responds, else a second round trip with query, variables and hash will be done.

https://github.com/facebook/relay/blob/b7832555f390e6acf965fe7fdc5eabab0ffcd4a8/packages/relay-runtime/store/RelayModernEnvironment.js#L274

https://github.com/facebook/relay/blob/4343e80b48ad21d7bc40b57abdcb9acb751c45b3/packages/relay-compiler/language/javascript/formatGeneratedModule.js#L45

Other possibility could be using something similar to "persist-output", but this removes the text of the operation, we need to keep the `text` and get also the `id` to use this one as hash.

@josephsavona Do you have some hint? is this doable? willing to work in a PR if it makes sense for you.

Start with RelayModernEnvironment.js at the linked fetchQuery entry point and formatGeneratedModule.js where generated operation metadata is formatted. Trace how params, text, and hashes are currently exposed; done means the operation can provide a cacheable hash or id while retaining the query text for the proposed request flow.

Written by the indexing model from the issue text.