Create "Authentication and authorization" section with configuration examples (basic auth, OIDC, Keycloak)

Consider linking to https://docs.camunda.io/docs/next/apis-tools/orchestration-cluster-api-rest/orchestration-cluster-api-rest-authentication/#authentication-support-matrix
# Changes
basic-auth: https://github.com/camunda/camunda-docs/pull/6781
internal keycloak:  https://github.com/camunda/camunda-docs/pull/6824
oidc: todo