[v3] Add Convenience Components

[bendvc]

Description

Gus ticket

This PR adds 2 (two) convenience components to the retail-react-app in order to allow those wanting to extend their template using the new extension model. This PR is first of many changes or additions of convenience components that will make extending the template easier. What these components do it allow partner developers to customize the application in a more granular way without having to override large chunks of the base template.

The convenience components added in the PR are as follows:

1. app/components/_app/paritals/above-header.jsx: This component allows partners to add content app-wide above the navigation.
2. app/pages/product-list/partials/above-page-header.jsx: This components allows partners to add content above the plp page.

Changes

• Add new convenience components and updated the components they are used in.

How to Test-Drive This PR

Because by default these component don't have an implementation, follow these steps before to make them visible.

1. Do a global search for the following text Header = () => null and replace it with this:

Header = () => (
    <div style={{border: '1px solid black', backgroundColor: 'red'}}>Custom Content</div>
)
import React from 'react'

2. In the "template-retail-react-app" run npm start
3. In the browser that was opened navigate to the following url http://localhost:3000/global/en-GB/category/womens
4. You should see the below screen capture which highlights the placement of these convenience components bay making them visible. Once template extensibility is merged we can now override those components with new implementations as see them on the app/plp.

Checklists

General

• CHANGELOG.md updated with a short description of changes (not required for documentation updates)

[bfeister]

For me, there's only one that stood out and is not included here – namely something along the lines of belowNavbar or something because I think that's a common spot for a site wide banner that is context aware or something

Let's disregard this suggestion, touched base with Nathan and I don't want to interfere in terms of "what's on the menu" for Template Hooks, I'm good for now

[kevinxh]

If you want to have <AboveHeader /> show for checkout, better move it up and out from the condition !isCheckout ? ...