[agent][property type] Change allowed_tools to Set as Duplicate doesn’t make sense

[skcoirz]

• ActionAgent has a property called, allowed_tools, which is declared as List. It stores all provided tools which is available to use during agent action.
• This collection shouldn’t allow duplicates. The original datatype List doesn’t make sense. Each tool should be unique. Even when there are variants (assuming in the future), it would be named differently in load_tools.