Create editor skeleton on add/edit product pages

[joshuatf]

There is some prior art for the initial editor skeleton and framework in this POC PR.

This issue will involve adding the base editor components for use with a couple of placeholder blocks.

Note that we can probably combine the add/edit product pages into a single page/component this time instead of creating 2 separate addProductPage and editProductPage components.

Updating the routes of the current editor will be done as part of this issue: #36989

Acceptance criteria

• The skeleton editor shows some placeholder blocks until the other blocks are ready to be added
• Visiting the add product page should show the new skeleton editor
• Visiting the edit product page should show the new skeleton editor

[joshuatf]

Estimate: 2

A lot can be pulled from the POC PR linked above, but I'm estimating a 2 to account for time to understand how this gets hooked up and works. Also we may have some React type conflicts again with pnpm that could elongate this issue.

[louwie17]

Changing it to a 3 to be cautious.

I do propose that we should replace the current product editor routes and pointing to this Component, but as part of this issue to create an additional route for the old editor (just for now, so we could still test things between the old and new editor as I could see that being beneficial).
I noticed there is actually a separate issue for tackling this: #36989