KKP: Improvement on OIDC Provider Configuration Doc

It would be nice to see if the below points get addressed in the existing doc https://docs.kubermatic.com/kubermatic/main/tutorials-howtos/oidc-provider-configuration/

```[tasklist]
### Tasks
- [ ] Improvisation on the Custom Configuration, calling out that the details available for KeyCloak explicitly
- [ ] Seed Configuration - Should it be separated out from Custom Configuration? Bit confusing since under custom configuration we are trying to explain KeyCloak changes for API and UI configuration and then at Seed configuration we are talking about dex.
- [ ] Unclear documentation - OIDC auth for KKP dashboard (https://docs.kubermatic.com/kubermatic/v2.23/tutorials-howtos/oidc-provider-configuration/) should be clearly distinguished from Share Clusters via Delegated OIDC Authentication ( https://docs.kubermatic.com/kubermatic/v2.23/tutorials-howtos/oidc-provider-configuration/share-clusters-via-delegated-oidc-authentication/)
- [ ] No field description of KubermaticAuthConfiguration ( https://docs.kubermatic.com/kubermatic/v2.23/references/crds/#kubermaticauthconfiguration).
- [ ] Add note on how to skip Dex chart installation if it has been replaced completly.
```

Start with the OIDC Provider Configuration documentation at the linked current and v2.23 URLs, then compare its Custom Configuration, Seed Configuration, delegated authentication, and KubermaticAuthConfiguration references. Done means the five listed documentation gaps are addressed, including the Dex chart installation note, with the dashboard and delegated-authentication topics clearly separated.

Written by the indexing model from the issue text.