Vendure provider (#223)

* Minimal list/detail views working with Vendure

* Implement useCart/useAddItem

* Implement useUpdateItem & useRemoveItem

* Implement useSearch

* Add operations codegen, tidy up

* Dummy checkout page

* Implement auth/customer hooks

* Use env var for Shop API url

* Add some documentation

* Improve error handling

* Optimize preview image size

* Fix accidental change

* Update Vendure provider to latest changes

* Vendure provider: split out gql operations, remove unused files

* Update Vendure provider readme

* Add local next.config to Vendure provider, update docs

* Update to use demo server

* Fix build errors

* Use proxy for vendure api

* Simplify instructions in Vendure readme

* Refactor Vendure checkout api handler

* Improve image quality

framework/vendure/auth/use-logout.tsx

@@ -0,0 +1,32 @@
+import { useCallback } from 'react'
+import { MutationHook } from '@commerce/utils/types'
+import useLogout, { UseLogout } from '@commerce/auth/use-logout'
+import useCustomer from '../customer/use-customer'
+import { LogoutMutation } from '../schema'
+import { logoutMutation } from '../lib/mutations/log-out-mutation'
+
+export default useLogout as UseLogout<typeof handler>
+
+export const handler: MutationHook<null> = {
+  fetchOptions: {
+    query: logoutMutation,
+  },
+  async fetcher({ options, fetch }) {
+    await fetch<LogoutMutation>({
+      ...options,
+    })
+    return null
+  },
+  useHook: ({ fetch }) => () => {
+    const { mutate } = useCustomer()
+
+    return useCallback(
+      async function logout() {
+        const data = await fetch()
+        await mutate(null, false)
+        return data
+      },
+      [fetch, mutate]
+    )
+  },
+}