Support more static website generators

[hacdias]

Right now, cady-hugo is capable of editing, creating and uploading files to the file system, similar to a CMS. Those functionalities are transversal to all of the static website generators.

So, the idea is to change the name of the plugin and make it more global, like caddy-cms. It would have an option to use Hugo or use an external static website generator.

I think it would be simple to do because the only Hugo command used inside the plugin is to regenerate the website. As Hugo is builded with Go, it offers a better experience with Caddy in this case.

To support others static website generators, we would have these options:

cms {
     external true        # default false
     command jekyll       # the command with all of the needed flags
}```