`relative_entropy` doesn't support constants which aren't wrapped in `constant`

julia> using Convex

julia> N = 10
10

julia> b = rand(N)
10-element Vector{Float64}:
 0.13262633847871297
 0.9254408726815795
 0.13936575019827857
 0.3329759851512133
 0.5964209280418487
 0.8590087709390417
 0.7599860068305675
 0.841494184551078
 0.1349705410637151
 0.017608754157530382

julia> x = Variable(10)
Variable
size: (10, 1)
sign: real
vexity: affine
id: 493…512

julia> relative_entropy(b, x)
ERROR: MethodError: no method matching relative_entropy(::Vector{Float64}, ::Variable)

Closest candidates are:
  relative_entropy(::Convex.AbstractExpr, ::Convex.AbstractExpr)
   @ Convex ~/.julia/packages/Convex/y7lu0/src/atoms/RelativeEntropyAtom.jl:53

Stacktrace:
 [1] top-level scope
   @ REPL[72]:1

julia> relative_entropy(constant(b), x)
relative_entropy (convex; real)
├─ 10×1 Matrix{Float64}
└─ 10-element real variable (id: 493…512)

We should add some methods to add constant automatically.

jump-dev / Convex.jl

`relative_entropy` doesn't support constants which aren't wrapped in `constant` #694