Use Pydantic for action argument validation & property models

[VigneshVSV]

Currently there are two ways to validate arguments given to actions

• Using JSON schema validation (which is alright)
• parameterized function, which is a little verbose.

Best is to use type annotations as much as possible. Its succint & mostly understandable.

There is an implementation in labthings-fastapi. Once the GPL related license details are sorted out, it can be carried over.

Its also better to describe actions using objects instead of a descriptor. One may have to create an Action class, which are instantiated for each action.

Regarding property models, many are comfortable using pydantic based models which will also offer a different type of flexibility compared to param. This should be supported. Code is already there in labthings-fastapi.