Update authentication mechanism - code and docs

[simcod]

As possible authentication mechanism, we should better document the OIDC configuration. In this context, the dex-specific configurations and codes should be removed. These can be found in the following repositories (no claim to be complete):

security

• here
• here

---

metal-api

• here

---

metal-roles

• here
• here

---

masterdata-api

• here

---

helm-charts

• here

---

metalctl

• here

---

metal-lib

• here