feat(medusa, medusa-js, medusa-react): Implement Sales Channel list (#1815)

**What**
Support sales channel list in medusa, medusa-js and medusa-react

**How**

By implementing a new endpoint and the associated service method as well as the repository methods.

Medusa-js new list method in the resource

Medusa-react new hook in the queries

**Tests**

Endpoint test
Service test
Integration test
Hook tests

Fixes CORE-280

packages/medusa-react/mocks/data/fixtures.json

@@ -1270,6 +1270,15 @@
       "updated_at": "2022-07-05T15:16:01.959Z",
       "created_at": "2022-07-05T15:16:01.959Z",
       "deleted_at": null
-    }
+    },
+    "sales_channels": [{
+      "id": "sc_01F0YES4R67TXXC1QBQ8P54A8Y",
+      "name": "sales channel 1 name",
+      "description": "sales channel 1 description",
+      "is_disabled": false,
+      "updated_at": "2022-07-05T15:16:01.959Z",
+      "created_at": "2022-07-05T15:16:01.959Z",
+      "deleted_at": null
+    }]
   }
 }

packages/medusa-react/mocks/handlers/admin.ts

@@ -1682,6 +1682,18 @@ export const adminHandlers = [
     )
   }),
 
+  rest.get("/admin/sales-channels", (req, res, ctx) => {
+    return res(
+      ctx.status(200),
+      ctx.json({
+        count: 1,
+        limit: 20,
+        offset: 20,
+        sales_channels: fixtures.get("sales_channels"),
+      })
+    )
+  }),
+
   rest.post("/admin/sales-channels/:id", (req, res, ctx) => {
     return res(
       ctx.status(200),