Add documentation and sample for OpenApi configuration

[64J0]

Description:

Follow-up from this PR: https://github.com/giraffe-fsharp/Giraffe/pull/599.

We basically need:

• Some paragraphs explaining how this configuration works and how to use it;
• A new sample project.

[nojaf]

@64J0 are you also on board with moving https://github.com/mrtz-j/Giraffe.OpenApi to https://github.com/giraffe-fsharp?

[64J0]

@64J0 are you also on board with moving https://github.com/mrtz-j/Giraffe.OpenApi to https://github.com/giraffe-fsharp?

@nojaf +/-, I know the intention exists, but I'm not aware of how the move process is going.

[nojaf]

Well @mrtz-j would need to transfer it (via https://github.com/mrtz-j/Giraffe.OpenApi/transfer) to giraffe-fsharp.

Once that happens I believe some administrator in that organization would need to accept and that would move it. A next step would then be to setup NuGet publishing similar to how it work for the other packages in Giraffe.

[mrtz-j]

I am ready to transfer it. I just need to know if I need to be invited into the organization or if I can simply transfer it and then create PRs to finish the Nuget-setup/README.

[nojaf]

Did you try

[mrtz-j]

Yes. I tried to do that, but I got the following error message: You don’t have the permission to create public repositories on giraffe-fsharp.

[nojaf]

Ok, I see. Could you add me as administrator to the repo? I believe I'm admin in the giraffe-org

[nojaf]

@mrtz-j thanks for the invite, I need to be admin on that repo as well to transfer it.

[mrtz-j]

It seems that I can only give you write/read access, but not admin. I'll try to transfer the repo to you instead, and then you can add it to the Giraffe org.

[64J0]

Imported the repo here: https://github.com/giraffe-fsharp/Giraffe.OpenApi.

[mrtz-j]

I've added some documentation and update the sample app here. It will use the available ENV-variables to push it to NuGet.