script to create pre-filled luarocks-tag-release workflow

[teto]

@vhyrro proposed to streamline the creation of PRs adding luarocks-tag-release to neovim plugins.

while I am not fan of the idea of automatically creating hundreds of PRs, having a script like https://github.com/teto/gh2rockspec for luarocks-tag-release could be nice. There is a bunch of plugins for which I would like to open such PRs and that would streamline it, minus the external dependencies that would need to be added manually (after initial push for instance).