Client: add validation for QiskitFunction and other dataclasses

[IceKhan13]

What is the expected enhancement?

Add validation rules for QiskitFunction and other dataclasses.

Something along those lines

@dataclass
class QiskitFunction:
  ...
  
  def __post_init__(self):
    if not self.entrypoint and not self.image:
      raise ValueError("Either entrypoint or image must be specified")
   if self.entrypoint and self.image:
      warining("Both entrypoint and image was provided. Entrypoint will be ignored as image has fixed entrypoint.")