Example config OIDC improvements

[busybox11]

Not 100% certain that those changes are relevant. As of now, they would've been useful to me when setting Headplane up as the documentation does not always follow the new config requirements, and the logging (or lack thereof) doesn't always show what could go wrong.

In my case, I got stuck between a faulty deployments that wouldn't update my server's config file for Headplane and Headscale, and Headplane itself not logging anything different when the config got finally saved in the server.

I was confused and thought the oidc section was intended to be indented at the same level as proc, when it shoud've been at the top level instead. Having fixed this, I had to spend some time debugging my SSO not being registered, which turned out to be a misconfiguration of the issuer field.

After having fixed all of those issues, Headplane did show helpful logging about missing config entries which are not documented yet.

From what I understand going through some OIDC-related issues, some OIDC-related changes will be required but some of them are still in progress and/or unsure. I did not include them here, and only focused on changes I believe would be helpful both for earlier versions and future ones.

Feel free to tell me if I got anything wrong along the way - which again is very likely haha. Most of my issues with Headplane were caused by a pile of other unrelated issues, so I might not have a full, clear picture in mind.

[tale]

Please fix the formatting

[busybox11]

Right, my MD formatter in Neovim resets the indentation no matter what. Had to do it inside the comments