omit "user_defined_ration_percentages" entry when rations are to be calculated by RuFaS

[RamiALBASHA]

The current behavior of RuFaS is to expect the user to provide the initial estimates of the ration percentages, even if it is up to RuFaS to calculate these percentages (animal.ration.user_input: false). Such behavior obliges the user to provide its own estimate of the ration, although this is what he/she is looking for. Besides, providing dummy values for percentages is likely to result in non-convergence issues with the ration optimizer.
It would be greatly useful to allow users to omit the feed.user_defined_ration_percentages entry when rations are to be estimated by RuFaS.

[KFosterReed]

Thanks for brining this to our attention @RamiALBASHA! I can confirm that RuFaS should be able to run without a user-defined diet and that on dev, it currently does not! I am going to huddle with @JoeWaddell and come up with a plan.

[KFosterReed]

Update! @JoeWaddell is on the job! He opened draft PR #2655 which should bring us back to being able to use the model in automated ration formulation mode without the user-defined percentages to initialize the optimizer algorithm.

That said, without any guidance at all, the automated diet formulation methods can come up with some very strange diets that are not likely to be fed on farms. We are going to continue to improve this on our end but in the meantime, I would recommend modifying the upper and lower bounds in the feed library CSV inputs of the feeds you're using to help 1) ensure you're including all the feeds you want to include, and 2) you end up with more reasonable diets. Also, using realistic prices will be important as well.