Add logviewer OAuth2 provider/application and akP-logviewer-admin permission

The ClickHouse log UI (logviewer) is being exposed at
https://logviewer.unkin.net behind oauth2-proxy in the logging namespace;
this adds the Authentik side as the prerequisite.

- Adds config/providers_oauth2/logviewer.yaml mirroring traefik: confidential
  client, client_id logviewer, secret from Vault kv
  kubernetes/namespace/logging/default/oauth-credentials,
  openid/email/profile scopes (ak_groups is attached to every oauth2
  provider by the module), strict redirect URI for the
  logviewer oauth2 callback.
- Adds config/permissions/akP-logviewer-admin.yaml bound to the logviewer
  application and nests it under akR-global-admin.

config/roles/akR-global-admin.yaml

@@ -4,6 +4,7 @@ permissions:
   - akP-argocd-admin
   - akP-rancher-admin
   - akP-litellm-admin
+  - akP-logviewer-admin
   # arrstack has no admin tier (it is a proxy front door); grant global admins
   # the front door plus every per-app entitlement so they reach all media apps.
   - akP-arrstack-user