docs: update api urls (#2074)

* Update homepage.md

* Update add-fulfillment-provider.md

* Update gatsby-medusa-starter.md

* Update how-to-create-notification-provider.md

* Update how-to-create-payment-provider.md

* Update how-to-implement-checkout-flow.mdx

* Update nextjs-medusa-starter.md

* Update paypal.md

* Update quick-start.md

* Update stripe.md

* Update docs/content/advanced/backend/shipping/add-fulfillment-provider.md

Co-authored-by: Shahed Nasser <shahednasser@gmail.com>

* Update docs/content/quickstart/quick-start.md

Co-authored-by: Shahed Nasser <shahednasser@gmail.com>

* Update docs/content/advanced/backend/shipping/add-fulfillment-provider.md

Co-authored-by: Shahed Nasser <shahednasser@gmail.com>

Co-authored-by: Danijel Predojevic <danijel@vivant.eco>
Co-authored-by: Shahed Nasser <shahednasser@gmail.com>

docs/content/quickstart/quick-start.md

@@ -81,5 +81,5 @@ You can learn more about configuring your server and loading environment variabl
 
 - Install our [Next.js](../starters/nextjs-medusa-starter) or [Gatsby](../starters/gatsby-medusa-starter) storefronts to set up your ecommerce storefront quickly.
 - Install the [Medusa Admin](../admin/quickstart.md) to supercharge your ecommerce experience with easy access to configurations and features.
-- Check out the [API reference](https://docs.medusajs.com/api) to learn more about available endpoints available on your Medusa server.
+- Check out the [API reference](https://docs.medusajs.com/api/store) to learn more about available endpoints available on your Medusa server.
 - Install [plugins](https://github.com/medusajs/medusa/tree/master/packages) for features like Payment, CMS, Notifications, among other features.