GreenField: Notifications API (#2055)

* GreenField: Notifications API

This refactors notifications so that we dont have a bunch of duplicated direct access to db contexts in controllers and then introduces new endpoints to fetch/toggle seen/remove  notifications of the current user.

* add tests + docs

* fix test

* pr changes

* fix permission json

BTCPayServer.Client/BTCPayServerClient.Notifications.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+using BTCPayServer.Client.Models;
+
+namespace BTCPayServer.Client
+{
+    public partial class BTCPayServerClient
+    {
+        public virtual async Task<IEnumerable<NotificationData>> GetNotifications(bool? seen = null,
+            CancellationToken token = default)
+        {
+            var response =
+                await _httpClient.SendAsync(
+                    CreateHttpRequest($"api/v1/users/me/notifications",
+                        seen != null ? new Dictionary<string, object>() {{nameof(seen), seen}} : null), token);
+            return await HandleResponse<IEnumerable<NotificationData>>(response);
+        }
+
+        public virtual async Task<NotificationData> GetNotification(string notificationId,
+            CancellationToken token = default)
+        {
+            var response = await _httpClient.SendAsync(
+                CreateHttpRequest($"api/v1/users/me/notifications/{notificationId}"), token);
+            return await HandleResponse<NotificationData>(response);
+        }
+
+        public virtual async Task<NotificationData> UpdateNotification(string notificationId, bool? seen,
+            CancellationToken token = default)
+        {
+            var response = await _httpClient.SendAsync(
+                CreateHttpRequest($"api/v1/users/me/notifications/{notificationId}",
+                    method: HttpMethod.Put, bodyPayload: new UpdateNotification() {Seen = seen}), token);
+            return await HandleResponse<NotificationData>(response);
+        }
+
+        public virtual async Task RemoveNotification(string notificationId, CancellationToken token = default)
+        {
+            var response = await _httpClient.SendAsync(
+                CreateHttpRequest($"api/v1/users/me/notifications/{notificationId}",
+                    method: HttpMethod.Delete), token);
+            await HandleResponse(response);
+        }
+    }
+}