Feat 494 email (#1472)

* docs: add english doc for email service

* docs: add norwegian doc for Email

* docs: refactor email docs after review comments

* docs: refactor email docs after review comments for the en-docs

---------

Co-authored-by: HauklandJ <[email protected]>
Co-authored-by: Eirik Mikkelsen <[email protected]>

content/app/development/configuration/email/_index.en.md

@@ -0,0 +1,33 @@
+---
+title: Email
+description: How to create custom email notifications for apps.
+weight: 400
+---
+
+## Activate generation of email notifications in your application
+
+The email client is automatically added to the application. To use it, inject the `IEmailNotificationClient`-interface. The interface defines a method used to order an email notification from the [Altinn Notifications](https://github.com/Altinn/altinn-notifications) API.
+
+### Code example
+```csharp
+using Altinn.App.Core.Internal.Email;
+using Altinn.App.Core.Models.Email;
+using Altinn.Platform.Storage.Interface.Models;
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace Altinn.App.Custom;
+
+public class CustomEmailClass(IEmailNotificationClient emailNotificationClient)
+{
+    private readonly IEmailNotificationClient _emailNotificationClient = emailNotificationClient;
+
+    public async Task OrderEmail(string subject, string body, List<EmailRecipient> emailRecipients, string sendersReference)
+    {
+        var emailNotification = new EmailNotification(subject, body, emailRecipients, sendersReference);
+        var emailOrderResponse = await _emailNotificationClient.Order(emailNotification, new System.Threading.CancellationToken());
+        ...
+    }
+}
+```

content/app/development/configuration/email/_index.nb.md

@@ -0,0 +1,33 @@
+---
+title: E-post
+description: Hvordan opprette egendefinerte e-postvarslinger for apper.
+weight: 400
+---
+
+## Aktiver generering av e-postvarslinger i applikasjonen din
+
+E-postklienten legges automatisk til i applikasjonen. For å bruke den, injiser `IEmailNotificationClient`-interface. IEmailNotificationClient definerer en metode som brukes til å bestille en e-postvarsling fra [Altinn Notifications](https://github.com/Altinn/altinn-notifications) API.
+
+### Kodeeksempel
+```csharp
+using Altinn.App.Core.Internal.Email;
+using Altinn.App.Core.Models.Email;
+using Altinn.Platform.Storage.Interface.Models;
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace Altinn.App.Custom;
+
+public class CustomEmailClass(IEmailNotificationClient emailNotificationClient)
+{
+    private readonly IEmailNotificationClient _emailNotificationClient = emailNotificationClient;
+
+    public async Task OrderEmail(string subject, string body, List<EmailRecipient> emailRecipients, string sendersReference)
+    {
+        var emailNotification = new EmailNotification(subject, body, emailRecipients, sendersReference);
+        var emailOrderResponse = await _emailNotificationClient.Order(emailNotification, new System.Threading.CancellationToken());
+        ...
+    }
+}
+```