Validate optics improvements

[GernotMaier]

The validate_optics application is among the first written for simtools!

It requires a bit of attention with the following suggestions for improvement:

• export effective focal length as model parameter (typical json, add metadata)
• calculate effective focal length as average over all simulated stars at different offsets
• add errors (and error propagation) to image centroids and effective focal length calculation
• move application code from validate_optics into module code
• move plotting code from the psf / ray_tracing modules to visualization submodules
• add integration tests for the different run modes of validate-optics (e.g. external file with star positions)

See also PR #2054