GET to /management/plugins returns nothing useful

[tiberio-baptista]

          > I did find an issue with `ServicesServlet`: though I'm not sure that this was present before, I noticed that `GET /management/plugins/` returns the following response body:

{
  "isRunning": false,
  "port": -1,
  "autostart": false
}

Please confirm if this is expected. Otherwise, the PR is good and I can approve.

Personally, I would expect this endpoint to list the available plugins.

That is a curious finding. That endpoint is not part of the API, but it was probably captured by the service status servlet anyway, which tried to fetch the status of a service which does not exist.

This can be improved, but it is hardly problematic, nor does it not look like a regression from this PR.

Originally posted by @Enet4 in #705 (comment)

[Enet4]

I had a second look at this. There were plans to support /management/plugins/ in the early v2 stages, but it was never done. It was only mapped into a stub in ServicesServlet, which in turn was designed to inspect and manipulate the status of DICOM services.

What we do have now is /plugins, which serves the purpose better.

I say we ditch the /management/plugins/ endpoint, so that it is not confused with the DICOM Storage and Query/Retrieval service status endpoints.