API v2 update customer

[c8y3]

Implement endpoint PUT /api/v2/manage/customers/{identifier} to update a customer.

• return 200 in case of success
• create method in business layer
• update a field
• return 400 when a field is in incorrect format
• return 403 when the user is denied permission
• return 404 when the resource is not found
• check returned object is uniform with other endpoints
• deprecate POST /manage/customers/update/<int:client_id>
• openapi: document endpoint
• openapi: deprecate POST /manage/customers/update/<int:client_id>