feat(gc): gc after HTTP calls and after runs

[pankgeorg]

heavily borrowed ideas from https://github.com/JuliaComputing/HTTPQuickstart.jl/blob/main/src/server.jl

requires JuliaPluto/Malt.jl#88 to actually gc on the worker

Try this Pull Request!

Open Julia and type:

julia> import Pkg
julia> Pkg.activate(temp=true)
julia> Pkg.add(url="https://github.com/fonsp/Pluto.jl", rev="pg/gc")
julia> using Pluto