docs: rearrange user guide (#2127)

* added lists guide

* restructure existing guides

* added new pages after restructuring

* added blank pages + rearranged sidebar

docs/content/user-guide/regions/providers.md

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+# Manage Payment and Fulfillment Providers
+
+In this document, you’ll learn how to manage a region’s payment and fulfillment providers in your Medusa Admin.
+
+## Overview
+
+You can choose the payment and fulfillment providers available in each region. This allows you to provide customers in specific regions the providers that are available in their country or region.
+
+When a payment or fulfillment provider is added to a region, it means a customer is able to select that payment or fulfillment provider during checkout to complete their purchase.
+
+---
+
+## Manage Payment Providers
+
+To add or remove a payment provider in a region:
+
+1. Go to Settings → Regions.
+2. Select a region to edit.
+3. Scroll down to the Payment Providers section in the Details form.
+4. Select the payment providers you want to add to the region.
+5. Unselect the payment providers you want to remove from the region.
+6. Click Save.
+
+---
+
+## Manage Fulfillment Providers
+
+To add or remove a fulfillment provider in a region:
+
+1. Go to Settings → Regions.
+2. Select a region to edit.
+3. Scroll down to the Fulfillment Providers section in the Details form.
+4. Select the fulfillment providers you want to add to the region.
+5. Unselect the fulfillment providers you want to remove from the region.
+6. Click Save.