API v2 get paginated customers

[c8y3]

Implement endpoint GET /api/v2/manage/customers to get a paginated list of customers

• successful GET should return 200
• field data should be present
• fields data should be [] when there are no customers
• field total should return 0 when there are no customers
• field total should return 1 when there is a customer
• it should accept page, per_page parameters
• it should accept order_by and sort_dir parameters
• it should return 400 when the field specified on order_by does not exist on customers
• fields last_page, current_page and next_page should be present in result
• introduce a method at the business level
• use object PaginationParameter
• check returned object is uniform with other endpoints, use the correct schema object
• deprecate GET /manage/customers/list
• openapi: document endpoint
• openapi: deprecate GET /manage/customers/list