Add IntegrationInterface documentation

[opr]

This PR adds documentation for the IntegrationInterface interface, and a mini-guide about how extension developers could use it.

Fixes #4209

How to test the changes in this Pull Request:

1. Read the documentation from a third-party extension developer's point of view and ensure it makes sense.
2. Verify any links work and resolve to the correct location

Changelog

Add documentation for the IntegrationInterface which extension developers can use to register scripts, styles, and data with WooCommerce Blocks.

[github-actions]

Size Change: 0 B

Total Size: 994 kB

ℹ️ View Unchanged

Filename	Size
build/active-filters-frontend.js	8.04 kB
build/active-filters.js	7.52 kB
build/all-products-frontend.js	34.9 kB
build/all-products.js	36.7 kB
build/all-reviews.js	9.34 kB
build/atomic-block-components/add-to-cart--atomic-block-components/button--atomic-block-components/image---a7e2bb9b.js	2.51 kB
build/atomic-block-components/add-to-cart--atomic-block-components/button.js	2 kB
build/atomic-block-components/add-to-cart--atomic-block-components/image--atomic-block-components/title.js	335 B
build/atomic-block-components/add-to-cart-frontend.js	8.67 kB
build/atomic-block-components/add-to-cart.js	7.74 kB
build/atomic-block-components/button-frontend.js	1.73 kB
build/atomic-block-components/button.js	843 B
build/atomic-block-components/category-list-frontend.js	470 B
build/atomic-block-components/category-list.js	478 B
build/atomic-block-components/image-frontend.js	1.65 kB
build/atomic-block-components/image.js	1.31 kB
build/atomic-block-components/price-frontend.js	2.05 kB
build/atomic-block-components/price.js	2.07 kB
build/atomic-block-components/rating-frontend.js	520 B
build/atomic-block-components/rating.js	524 B
build/atomic-block-components/sale-badge-frontend.js	470 B
build/atomic-block-components/sale-badge.js	474 B
build/atomic-block-components/sku-frontend.js	390 B
build/atomic-block-components/sku.js	394 B
build/atomic-block-components/stock-indicator-frontend.js	568 B
build/atomic-block-components/stock-indicator.js	573 B
build/atomic-block-components/summary-frontend.js	906 B
build/atomic-block-components/summary.js	911 B
build/atomic-block-components/tag-list-frontend.js	467 B
build/atomic-block-components/tag-list.js	472 B
build/atomic-block-components/title-frontend.js	1.43 kB
build/atomic-block-components/title.js	1.28 kB
build/attribute-filter-frontend.js	17.8 kB
build/attribute-filter.js	11.4 kB
build/blocks-checkout-editor.js	10.6 kB
build/blocks-checkout.js	19.9 kB
build/cart-frontend.js	78.6 kB
build/cart.js	45.3 kB
build/checkout-frontend.js	82.6 kB
build/checkout.js	47.4 kB
build/featured-category.js	7.3 kB
build/featured-product.js	9.47 kB
build/handpicked-products.js	6.03 kB
build/price-filter-frontend.js	14.2 kB
build/price-filter.js	9.37 kB
build/price-format.js	1.38 kB
build/product-best-sellers.js	6.19 kB
build/product-categories.js	3.39 kB
build/product-category.js	7.06 kB
build/product-new.js	6.35 kB
build/product-on-sale.js	6.69 kB
build/product-search.js	2.68 kB
build/product-tag.js	6.18 kB
build/product-top-rated.js	6.32 kB
build/products-by-attribute.js	7.29 kB
build/reviews-by-category.js	11.2 kB
build/reviews-by-product.js	12.8 kB
build/reviews-frontend.js	9 kB
build/single-product-frontend.js	38.4 kB
build/single-product.js	9.71 kB
build/vendors--atomic-block-components/price-frontend.js	6.53 kB
build/wc-blocks-data.js	10.9 kB
build/wc-blocks-editor-style-rtl.css	14.9 kB
build/wc-blocks-editor-style.css	14.9 kB
build/wc-blocks-google-analytics.js	1.99 kB
build/wc-blocks-middleware.js	1.48 kB
build/wc-blocks-registry.js	2.75 kB
build/wc-blocks-shared-context.js	1.54 kB
build/wc-blocks-shared-hocs.js	1.74 kB
build/wc-blocks-style-rtl.css	19.1 kB
build/wc-blocks-style.css	19 kB
build/wc-blocks-vendors-style-rtl.css	1.05 kB
build/wc-blocks-vendors-style.css	1.05 kB
build/wc-blocks-vendors.js	242 kB
build/wc-blocks.js	3.51 kB
build/wc-payment-method-bacs.js	812 B
build/wc-payment-method-cheque.js	807 B
build/wc-payment-method-cod.js	903 B
build/wc-payment-method-paypal.js	844 B
build/wc-payment-method-stripe.js	12.4 kB
build/wc-settings.js	2.94 kB

_{compressed-size-action}

[mikejolley]

Looks great 👏🏻 I didn't spot anything needing changes. 🚢