Support for MathOptInterface

[ccoffrin]

No rush, just need an issue to track status.

[matbesancon]

one specificity of Pajarito is that it's directly a MPB.AbstractSolver type being used and exposed.
To bring MOI, several options:

1. Create a MOI.AbstractOptimizer type from scratch and implementing the methods on the side
2. Separating the inner working solver and wrapping it in both a MPB and a MOI wrapper separatly
3. Something else?

[matbesancon]

I was looking at the ECOS solver for comparison and realized the same approach was not obvious

[chriscoey]

an MOI rewrite of Pajarito is under development at https://github.com/chriscoey/MOIPajarito.jl

[chriscoey]

I brought that code into this repo on the new main (default) branch. It is a complete rewrite with a simpler design, and easily extensible for new cones (see PajaritoExtras.jl for more cones and examples).