Implement update service for v2 approval rules

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Implement update service for v2 approval rules.

Requirements:

• Check authorisation
• Find the approval rule by ID
• Update rule attributes (name, approvals_required)
• Update user approvers (if user_ids provided)
• Update group approvers (if group_ids provided)
• Handle remove_hidden_groups parameter (filter inaccessible groups)
• Return ServiceResponse with success/error

Reference: POC implementation in poc/v2-approval-rules-complete branch