Add InfiniteOpt as an Extension

[dnguyen227]

Working version of #114 .

This adds an extension such that DisjunctiveProgramming is compatible with InfiniteOpt. It overloads the needed functions and provide the InfiniteGDPModel and InfiniteLogical functions.

A basic example is shown below:

using DisjunctiveProgramming, InfiniteOpt, HiGHS

# Create the model
model = InfiniteGDPModel(HiGHS.Optimizer)

# Create the infinite variables
I = 1:4
@infinite_parameter(model, t ∈ [0, 1], num_supports = 100)
@variable(model, 0 <= g[I] <= 10, Infinite(t))

# Add the disjunctions and their indicator variables
@variable(model, G[I, 1:2], InfiniteLogical(t))
@constraint(model, [i ∈ I, j ∈ 1:2], 0 <= g[i], Disjunct(G[i, 1]))
@constraint(model, [i ∈ I, j ∈ 1:2], g[i] <= 0, Disjunct(G[i, 2]))
@disjunction(model, [i ∈ I], G[i, :])

# Add the logical propositions
@variable(model, W, InfiniteLogical(t))
@constraint(model, G[1, 1] ∨ G[2, 1] ∧ G[3, 1] == W := true)
@constraint(model, 𝔼(binary_variable(W), t) >= 0.95) # incorporate binary variable of logical variable in a nonlogical constraint

# Reformulate and solve 
optimize!(model, gdp_method = Hull())

# check the results
value(W)

As of right now, Hull, BigM, Indicator, and PSplit methods will function. Cutting Planes and Multiple BigM methods will be added in the future.

[codecov-commenter]

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[pulsipher]

Just two minor questions