fix: Add default file permission (755 for image build) (#1176)

Author: HofmeisterAn

docs/api/create_docker_image.md

@@ -101,3 +101,14 @@ _ = new ImageFromDockerfileBuilder()
 !!!tip
 
     Testcontainers for .NET detects your Docker host configuration. You do **not** have to set the Docker daemon socket.
+
+## Known issues
+
+- When building an image using Testcontainers for .NET and switching the user's context (`USER` statement) in a Dockerfile, the user won't automatically become the [owner](https://github.com/testcontainers/testcontainers-dotnet/issues/1171#issuecomment-2099197840) of the working directory, which seems to be the case when building the image from the CLI. If the running process requires write access to the working directory, it is necessary to set the permissions explicitly (the base image in this example already contains the user `app`):
+
+   ```Dockerfile
+   FROM mcr.microsoft.com/dotnet/sdk:8.0
+   WORKDIR /app
+   RUN chown app:app .
+   USER app
+   ```

src/Testcontainers/Images/DockerfileArchive.cs

@@ -4,6 +4,7 @@ namespace DotNet.Testcontainers.Images
   using System.Collections.Generic;
   using System.IO;
   using System.Linq;
+  using System.Runtime.InteropServices;
   using System.Text;
   using System.Text.RegularExpressions;
   using System.Threading;
@@ -148,7 +149,12 @@ public async Task<string> Tar(CancellationToken ct = default)
               using (var inputStream = new FileStream(absoluteFilePath, FileMode.Open, FileAccess.Read))
               {
                 var entry = TarEntry.CreateTarEntry(relativeFilePath);
-                entry.Size = inputStream.Length;
+                entry.TarHeader.Size = inputStream.Length;
+
+                if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+                {
+                  entry.TarHeader.Mode = (int)Unix.FileMode755;
+                }
 
                 await tarOutputStream.PutNextEntryAsync(entry, ct)
                   .ConfigureAwait(false);