The connector Saved Object already supports authMode. We should leverage that field by inferring the mode from auth type metadata, rather than hardcoding auth type ids in application logic.

Goal

• Add an auth‑type configuration flag (e.g. authMode: 'per-user' | 'shared' or isPerUser: boolean) to the auth type spec.
• Use this metadata to infer and persist connector authMode on create/update.
• Do not hardcode oauth_authorization_code checks in application code; the auth type spec should be the source of truth.
• Today, only OAuth Authorization Code should be marked per‑user; all other auth types default to shared.

Constraint

• Prevent auth type changes on update for connectors already using a per‑user auth type (reject or ignore the change) to avoid a one‑way door before the best UX is confirmed. (doesn't need to be done in this PR, but taken into account if needed)

Outcome

• auth_mode is stored for connectors based on auth type metadata.
• The list/get APIs return auth_mode consistently for all connectors.