Added exception handler image processor decorator

[GermanHydrogen]

This is an alternative suggestion to implementing the exception handling in the image processor base class.
Doing this in the base class would introduce two new attributes suppress_exception: bool which toggles the exception handling and error_header: Optional[str] which defines the error header flat. This introduces the problem that the error_header attribute can be set without the suppress_exception attribute being true, which could lead to errors in config management.
The alternative decorator approach removes the need for the first attribute.
A config with this could look like this

[...]
pipeline:

  - class: pyobs.images.processors.detection.SepSourceDetection
  - class: pyobs.image.processors.ExceptionHandler
      processor:
        class: pyobs.images.processors.astrometry.AstrometryDotNet
          url: ...
          radius: 5
      error_header: "WCSERR"
[...]

I'm open to feedback.

[thusser]

Hmm, not a bad idea... But that moves error handling in the config file, which I find weird... The config also gets a lot more complex with this. What about adding that functionality to the ImageProcessor base class?