Make VerifyComplexAppSample Test a [Theory]

[lbussell]

Looking at the VerifyComplexAppSample test, there are two concerns:

1. The complexapp sample Dockerfile uses the multi-platform tags and therefore won't build on Windows in .NET 8 due to Switch multi-platform tags to Linux only #4492:

   dotnet-docker/samples/complexapp/Dockerfile

   Lines 1 to 3 in c09ce8b

   	# https://hub.docker.com/_/microsoft-dotnet
   	FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
   	WORKDIR /source

2. The test is a [Fact], and therefore runs once per leg but uses only one base image, the multi-platform image, which is Debian. The Dockerfile should be amended to support multiple different images and the test should be amended to test across supported operating systems like the other sample tests.

   dotnet-docker/tests/Microsoft.DotNet.Docker.Tests/SampleImageTests.cs

   Lines 92 to 93 in c09ce8b

   	[Fact]
   	public void VerifyComplexAppSample()

[mthalman]

[Triage]
The Dockerfile is meant to be a sample and the 8.0 tag was chosen for simplicity. Modifying the Dockerfile too drastically to support different test environments isn't really the approach we want. It's just a matter of making sure the Dockerfile can be built.

It's not necessary to provide a Windows-compatible Dockerfile as the main intent of the sample is to demonstrate a multi-project solution and how those get composed with a Dockerfile.