Allow measurement errors in photometry.DiskIntegratedPhaseFunc.from_obs method

[jianyangli]

This is a request for

• a new feature
• an enhancement to existing sbpy functionality
• somethings else: [explain here]

The requested changes will be implemented by

• me
• the sbpy developers

High-level concept
sbpy.photometry.DiskIntegratedPhaseFunc provides class method from_obs to fit observational data and retrieve a phase function model. The current implementation doesn't use measurement errors in the fit. This enhancement should allow the use of measurement errors if present in the input.

Explain the relevance to sbpy
Enhancement to existing sbpy class method.

Proposal details
Check the existence of measurement errors in the input, and pass to fitter if present.

Example (pseudo-)code