Help users convert unconverted values

Missing documentation or idea for new documentation.

Aviary lists all the FLOPS and GASP variables that have not been converted by the fortran_to_aviary converter function, but there is no information on the best way for a user to replicate the functionality of those variables in Aviary.
We should add a documentation page to assist with describing how to implement the functionality, link to examples if we have them and/or include small code snippets to help.

A good example is FLOPS AERIN.VAPPR which would add a constraint on the VAPP output variable.
In aviary there is no mapping of VAPPR so it is ignored during conversion.
It is easy to replicate this by adding a constraint in Aviary that Mission.Landing.INITIAL_VELOCITY >= VAPPR. This can be added with prob.model.add_constraint(Mission.Landing.INITIAL_VELOCITY, lower=145, ref=1e2) sometime before prob.setup().
Issue #1222 provides some discussion for this specific variable.

Issue with existing documentation.

No response

Start with the fortran_to_aviary converter and issue #1222 to understand how unconverted FLOPS and GASP variables are identified. Add a documentation page explaining how users can reproduce unmapped functionality, using FLOPS AERIN.VAPPR and the provided constraint example, with links or snippets where available. Done when users can follow the page to implement an unconverted variable in Aviary.