List customer entitlement balances with advanced filtering

Retrieve customer entitlement balances with comprehensive filtering, sorting, and pagination.

Filter by:

• Customer: customer, customer__in (filter by specific customer IDs).
• Entitlement: entitlement, entitlement__in (filter by specific entitlement IDs).
• Contract: contract_id, contract_id__in (filter by contract IDs - useful for contract-specific entitlements).
• Quantities: quantity, quantity_used with range filters (gt, gte, lt, lte, neq).
• Dates: created_at, active_from with range filters for time-based filtering.
• Status: Use quantity__gt=0 to show only active balances, or quantity_used__lt=quantity to show available balances.

Enrichment options (populate parameter):

• customer: Include customer name and email details.
• contract: Include contract name for entitlements granted by contracts.
• product: Include product name for product-specific entitlements.
• invoice: Include invoice number for invoice-generated entitlements.
• Multiple: Use comma-separated values like 'customer,contract,product,invoice' for full enrichment.

Pagination & sorting:

• limit: page size (1-100, default 50).
• cursor: pass 'next' from previous response to paginate.
• sort_key: field to sort by (id, created_at, quantity, quantity_used, active_from, expiry_at).
• sort_type: 'asc' or 'desc' (default 'asc').
• search: text search across entitlement names and descriptions.

Common use cases:

• Contract entitlements: Use contract_id filter to get all entitlements for a specific contract.
• Customer overview: Use customer filter with populate=contract,product for complete customer entitlement view.
• Low balance alerts: Use quantity__gt=0 and quantity_used__gte with percentage calculations.
• Expiring entitlements: Use expiry_at__lt with future date to find soon-to-expire entitlements.