Kubernetes ingress controller samples need improvement

### Some details
I recently tried the kubernetes ingress samples and although i got it working. The documentation in the [docs folder](https://github.com/microsoft/reverse-proxy/blob/main/docs/docfx/articles/kubernetes-ingress.md) could use some improvement. I ran into two concrete issues.

Firsts it talks about a dockerfile you can build in `.\src\Kubernetes.Controller\Dockerfile` but this file does not seem to exist, not even in the main branch. Can you give clarification on this?

Second I tried to build the dockerfile from the ingress sample `.\samples\KuberenetesIngress.Sample\Combined\Dockerfile`. But this kept getting stuck on step 12/16 trying to do a dotnet restore.
```
reverse-proxy git:(main) docker build . -t acrkasparinternalunivweu.azurecr.io/yarp-controller:1.0.0 -f ./samples/KubernetesIngress.Sample/Combined/Dockerfile
[+] Building 584.0s (20/26) docker:desktop-linux
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 1.53kB 0.0s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 461B 0.0s
=> [internal] load metadata for docker.io/amd64/buildpack-deps:jammy-curl 1.5s
=> [internal] load metadata for mcr.microsoft.com/dotnet/aspnet:6.0 0.0s
=> [auth] amd64/buildpack-deps:pull token for registry-1.docker.io 0.0s
=> [base 1/2] FROM mcr.microsoft.com/dotnet/aspnet:6.0 0.0s
=> [publish 1/16] FROM docker.io/amd64/buildpack-deps:jammy-curl@sha256:6c7cd91d715ab799960671f 0.0s
=> [internal] load build context 0.1s
=> => transferring context: 200.53kB 0.1s
=> CACHED [base 2/2] WORKDIR /app 0.0s
=> CACHED [final 1/2] WORKDIR /app 0.0s
=> CACHED [publish 2/16] WORKDIR /src 0.0s
=> CACHED [publish 3/16] COPY [global.json, ] 0.0s
=> CACHED [publish 4/16] RUN curl -sSL https://dot.net/v1/dotnet-install.sh | bash /dev/stdin - 0.0s
=> [publish 5/16] COPY [samples/KubernetesIngress.Sample/Combined/Yarp.Kubernetes.IngressContro 0.0s
=> [publish 6/16] COPY [src/ReverseProxy/Yarp.ReverseProxy.csproj, src/ReverseProxy/] 0.0s
=> [publish 7/16] COPY [src/Kubernetes.Controller/Yarp.Kubernetes.Controller.csproj, src/Kubern 0.0s
=> [publish 8/16] COPY [src/Directory.Build.props, src/] 0.0s
=> [publish 9/16] COPY [Directory.Build.*, ./] 0.0s
=> [publish 10/16] COPY [NuGet.config, ] 0.0s
=> [publish 11/16] COPY [eng/Versions.props, eng/] 0.0s
=> [publish 12/16] RUN /root/.dotnet/dotnet restore samples/KubernetesIngress.Sample/Combined/ 582.3s
=> => # Write your first app: https://aka.ms/dotnet-hello-world
=> => # Find out what's new: https://aka.ms/dotnet-whats-new
=> => # Explore documentation: https://aka.ms/dotnet-docs
=> => # Report issues and find source on GitHub: https://github.com/dotnet/core
=> => # Use 'dotnet --help' to see available commands or visit: https://aka.ms/dotnet-cli
=> => # --------------------------------------------------------------------------------------

```
This can go on exceeding 600 seconds at wich point i just give up.

The way to fix this for me was by introducing container properties in the `./samples/KuberenetesIngress.Sample/Combined/Yarp.Kubernetes.IngressController.csproj` file and leveraging Microsoft.NET.Build.Containers (Buillt into net7 sdk) to publish the project as a dockerfile.
```xml

net6.0;net7.0;net8.0
78d1f3b4-abce-4c5a-b914-3321fab1f8d0
Linux
$('System.TeamProject') != 'internal'

yarp-controller
1.0.0

```
`dotnet publish --os linux --arch x64 /t:PublishContainer -f net7.0 -c Release`

This worked great and built image `yarp-controller:1.0.0` locally.

Next I used `docker tag yarp-controller:1.0.0 my-container-registry.azurecr.io/yarp-controller:1.0.0` to tag it for the our Azure container registry.

Then i used `docker push my-container-registry.azurecr.io/yarp-controller:1.0.0` to push it to our container registry.

So my suggstion is to update the [doc](https://github.com/microsoft/reverse-proxy/blob/main/docs/docfx/articles/kubernetes-ingress.md) to
- leverage Microsoft.NET.Build.Containers so it works better.
- remove the first paragraph referencing `.\src\Kubernetes.Controller\Dockerfile` which does not exist
- include instructions for applying docker tag after the build so you don't run into docker registry authentication isues while building
- either update the paths to use / instead of \ or include seperate code blocks for MacOS/Linux users.

I am using a M2 Macbook Pro with .NET 7 and dockerdesktop 4.22.1

I would also like to ask if you would except a PR from me to improve this?

**How many backends are in your application?**

- [ ] 1-2
- [ ] 3-5
- [ ] 6-10
- [x] 10+

**How do you host your application?**

- [x] Kubernetes
- [ ] Azure App Service
- [ ] Azure VMs
- [ ] Other Cloud Provider (please include details below)
- [ ] Other Hosting model (please include details below)

### What did you think of YARP?
I am really impressed with the project so far but it lacks documentation. Especially in the route vs cluster concepts department.