Update oauth2-proxy readme for Keycloak

[juliusvonkohout]

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The following issues are related, because ...
#2931 (comment)

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[juliusvonkohout]

https://cloud-native.slack.com/archives/C073W572LA2/p1733818844895669
Hailey are you sure about
skip_auth_routes = [
"^/oauth2/callback",
]
? Please test again and review / comment on #2934

[juliusvonkohout]

CC @kromanow94

[juliusvonkohout]

"@Julius von Kohout
I tried removing that line but it still worked. When I first tried without this, I couldn't access to the dashboard, but this time I could without it. I'm not sure it is the thing that really matters. I figured I should find other factors."

[kromanow94]

Just a hunch - maybe it was connected to Istio where it needs some time to refresh it's settings from the cache and populate to the istio-proxy containers (or istio-cni). This action is done by istiod. I usually give it like 10 seconds before testing changes in configuration.