Greenfield: Improve store users API (#6427)

* Greenfield: Improve store users API

- Adds an endpoint to update store users (before they had to be removed ad re-added)
- Checks for the existance of a user and responds with 404 in that case (fixes #6423)
- Allows retrieval of user by user id or email for add and update (consistent with the other endpoints)
- Improves the API docs for the store users endpoints

* Swagger: Reuse UserIdOrEmail parameter component

* Add details to store user data

BTCPayServer.Client/BTCPayServerClient.StoreUsers.cs

@@ -29,4 +29,10 @@ public partial class BTCPayServerClient
         if (request == null) throw new ArgumentNullException(nameof(request));
         await SendHttpRequest<StoreUserData>($"api/v1/stores/{storeId}/users", request, HttpMethod.Post, token);
     }
+
+    public virtual async Task UpdateStoreUser(string storeId, string userId, StoreUserData request, CancellationToken token = default)
+    {
+        if (request == null) throw new ArgumentNullException(nameof(request));
+        await SendHttpRequest<StoreUserData>($"api/v1/stores/{storeId}/users/{userId}", request, HttpMethod.Put, token);
+    }
 }