feat: Allow fulfillment method type (and id) to be optional on Fulfillment method updates

[matthutchinson]

Fulfillment method type and id are now optional on Fulfillment Method update requests

Updates the schema to be more permissive, allowing fulfillment method type and id to be included in fulfillment method update requests (previously the schema defined this type with omit and id as required).

Consider this example scenario;

Changing a the type of fulfillment on an already created checkout. E.g. create checkout with only a pickup fulfillment method, but agent wishes to update this to an entirely new shipping fulfillment method in an update request. In this case type should be specified, but id would be omitted in the input.

Type of change

• New feature (non-breaking change which adds functionality)

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Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
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• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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[jingyli]

Thanks for catching this!

[matthutchinson]

cc @jingyli updated slightly to also make id optional here too, see updated example scenario in the PR description

[matthutchinson]

cc @jingyli / @richmolj just a nudge to see if we can merge this one?