fix(graphQL): Missing MediaType on dialog attachment url (#1264)

<!--- Provide a general summary of your changes in the Title above -->

## Description

<!--- Describe your changes in detail -->

## Related Issue(s)

- #1263

## Verification

- [ ] **Your** code builds clean without any errors or warnings
- [ ] Manual testing done (required)
- [ ] Relevant automated test added (if you find this hard, leave it and
we'll help out)

## Documentation

- [ ] Documentation is updated (either in `docs`-directory, Altinnpedia
or a separate linked PR in
[altinn-studio-docs.](https://github.com/Altinn/altinn-studio-docs), if
applicable)


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
- Introduced a new `mediaType` field in the `AttachmentUrl` type for
specifying the media type of attachments.
  
- **Bug Fixes**
- Corrected formatting issue by ensuring the `UUID` scalar type
definition ends with a newline character.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

docs/schema/V1/schema.verified.graphql

@@ -62,6 +62,7 @@ type Attachment {
 type AttachmentUrl {
   id: UUID!
   url: URL!
+  mediaType: String
   consumerType: AttachmentUrlConsumer!
 }
 
@@ -393,4 +394,4 @@ scalar DateTime @specifiedBy(url: "https:\/\/www.graphql-scalars.com\/date-time"
 
 scalar URL @specifiedBy(url: "https:\/\/tools.ietf.org\/html\/rfc3986")
 
-scalar UUID @specifiedBy(url: "https:\/\/tools.ietf.org\/html\/rfc4122")
+scalar UUID @specifiedBy(url: "https:\/\/tools.ietf.org\/html\/rfc4122")

src/Digdir.Domain.Dialogporten.GraphQL/EndUser/DialogById/ObjectTypes.cs

@@ -194,6 +194,7 @@ public sealed class AttachmentUrl
 {
     public Guid Id { get; set; }
     public Uri Url { get; set; } = null!;
+    public string? MediaType { get; set; }
 
     public AttachmentUrlConsumer ConsumerType { get; set; }
 }