Add FLARE-ON challenge

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### Details

I would like to have the binaries and solutions of the [FLARE-ON challenge](https://flare-on.com). My proposal is to:
- Add a new category, something like `Binaries`, where we could also move the current PMA labs.
- Add a `flare-on.vm` package which adds a `FLARE-ON` folder inside the new category with a subfolder per year with the binaries and solutions of that year.

Does someone know how big the binaries are? If the size if considerable, I would propose to have a package per year (`flare-on..vm`) and also add a `README.txt` to the `FLARE-ON` folder with short instructions about how to install the rest of the years. In the FLARE-VM default configuration we would then have only the last year.

In order to download the binaries and solutions, we need to make then available via a download URL, or is there such a URL in [flare-on.com](https://flare-on.com) already? :thinking:

I thought we had already an issue for this, but It doesn't look like there is one already (or at least I was not able to find it). In case this is a duplicate, please let me know.

Start by checking whether flare-on.com provides downloadable binaries and solutions, and determine the size of the available years. Then compare the proposed `flare-on.vm` package and per-year package options, including the new `Binaries` category and `README.txt`; done means the storage, download, and default-year approach is agreed.

Written by the indexing model from the issue text.