POST /notebookupload: allow specifying a filename

[fonsp]

You can now do POST /notebookupload?name=hello%20world and it will create a file like hello world 3.jl instead of Cute analysis 7.jl

[github-actions]

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="notebookupload-name")
julia> using Pluto