Feature/oauth2 proxy

[RichardLinde]

Added a general documentation for using a oauth2 proxy to secure services

[baumeister25]

IMHO the solution should be on a more abstract level.
In some parts it's very concrete (bitnami helm charts, localtest.me)

I think we should focus on 2 different things.
First: The overall concept. You sarted very good with the flow diagram. But you should also explain the diagram a bit and the flow without technical descriptions like deployments.

Then the different tools like you did: Keycloak, Oauth Proxies, Ingress
For each tool the configuration (as long as applicable for PROD and local) should be explained.
E.g. ingress routes (not the URLs, but what subroutes do i need and to which service do they direct) or e.g. the Oauth2 proxy settings. Where are they stored? How do they look like? Are they organized in a specific way or splitted, etc?

And last but not least as you already started a more concrete guide for the local deployment could be done. What is localTest.me, why do we need that. What about the specific configs, where to put them, etc.

[hohwille]

@RichardLinde thanks for this PR and your great contribution 👍
@baumeister25 what is the status here?
IMHO @RichardLinde has addressed your concerns (However, there is still a slight reference to keycloak at the ingress section that is still not so clear to me).
What also confuses me is that there is a broken image link image::OAuth2_Proxy-LocalProblem.drawio.svg[Localhost Problem] but that is already present before and not related to this PR at all.
It would be great if we can get this PR merged as IMHO it is already on the finishing line.

[baumeister25]

For me all images are working.
IMHO this can be merged.

[baumeister25]

Thanks for your work. I really like this article as it includes the most important points and links!