[V3] Remove cross-fetch from template-retail-react-app

[bendvc]

Description

We recently removed the commerce-api client code from the template, leaving behind the einstein implementation. Because einstein is only ever used on the client we don't need to use cross-fetch, so we are removing it in this PR.

Types of Changes

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Documentation update
• Breaking change (could cause existing functionality to not work as expected)
• Other changes (non-breaking changes that does not fit any of the above)

Changes

• Remove cross-fetch from useEinstein hook
• Fix tests to mock global fetch.
• Remove dep in package.json and re-lock

How to Test-Drive This PR

• Run tests, they should pass.
• Preview the template and navigate from page to page, you should see fetch logs for viewCategory viewProduct etc. This means things are still working.

General

• Changes are covered by test cases
• CHANGELOG.md updated with a short description of changes (not required for documentation updates)

[alexvuong]

Are we installing this package? Do we need this package? I tried this approach, and it does work without importing this library

let originalFetch

    beforeEach(() => {
        originalFetch = global.fetch
        global.fetch = jest.fn(() =>
            Promise.resolve({
                json: jest.fn(),
                ok: true
            })
        )
    })

    afterEach(() => {
        global.fetch = originalFetch
    })

[bendvc]

The lib was already installed and in dev dependancies. But I'm not sure what it was used for before. I think it was used before MSW as added maybe?

Anyway, it doesn't hurt to use a mock fetch lib that was already installed, rather than a one off mock. It might give more flexibility in the future if we have tests that do more than mock a successful call.