Add support for MOI.HermitianPositiveSemidefiniteConeTriangle

[araujoms]

If I create a model in JuMP with model = Model(Hypatia.Optimizer; add_bridges=false), add a Hermitian PSD variable @variable(model, [1:2, 1:2] in HermitianPSDCone()), and try to optimize it I get the error

"MathOptInterface.UnsupportedConstraint{MathOptInterface.VectorOfVariables, MathOptInterface.HermitianPositiveSemidefiniteConeTriangle}: MathOptInterface.VectorOfVariables-in-MathOptInterface.HermitianPositiveSemidefiniteConeTriangle constraint is not supported by the model"

But Hypatia supposedly does support it, see the documentation.

If I add instead @variable(model, [1:2, 1:2] in PSDCone()) it works as expected.

I opened this issue before in JuMP jump-dev/JuMP.jl#3306, but the dev @odow told me that it needs to be supported here, not there.

[chriscoey]

Hey @araujoms, yes - MOI only started supporting this set recently, so we will have to enable it through Hypatia's MOI interface. I'll have a look at that now.