Add support for fetching document metadata separately

Introduced a new `ReadDocumentDetailsQuery` to fetch document
metadata (`DocumentDetailsDto`) without the binary payload.
Updated `MappingProfile` to map `Document` to `DocumentDetailsDto`.

Refactored `DocumentService` to handle separate fetching of
metadata and binary data, combining them into `DocumentDto`.
Changed the metadata endpoint to `/api/Document/details`.

Added a new `GetDocumentDetails` endpoint in `DocumentController`
to return metadata without binary data. Updated
`EnvelopeReceiverPageDataService` with a new method
`GetDocumentMetadataOfSenderAsync` for fetching metadata.

These changes improve efficiency by allowing clients to load
metadata without transferring large binary data when unnecessary.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Services/EnvelopeReceiverPageDataService.cs

@@ -57,6 +57,14 @@ public class EnvelopeReceiverPageDataService(
         return await mediator.Send(new ReadDocumentQuery(EnvelopeId: envelopeId, UserId: user.SenderId()), cancellationToken);
     }
 
+    /// <summary>
+    /// Loads document metadata/elements for the authenticated sender without binary payload.
+    /// </summary>
+    public async Task<DocumentDetailsDto?> GetDocumentMetadataOfSenderAsync(ClaimsPrincipal user, int envelopeId, CancellationToken cancellationToken = default)
+    {
+        return await mediator.Send(new ReadDocumentDetailsQuery(EnvelopeId: envelopeId, UserId: user.SenderId()), cancellationToken);
+    }
+
     /// <summary>
     /// Loads the current receiver's signature placeholders.
     /// </summary>