Title pretty much explains.
I just re-downloaded RoM and i noticed that in C:\Program Files\Runes of Magic,
i remember there used to be a specific addon folder but its not present anymore.
Is this intentional?
C:\Program Files\Runes of Magic\Interface\Addons
If you use the Curse Client to download and install addons, it will create an Addons folder inside the Interface folder for you--along with unpacking and installing the addons themselves, in their own folders. If you download them manually (without the CC), you have to create the Addons folder yourself and follow whatever instructions the addon author gives.
And no, Gameforge doesn't support addons in any way, shape or form. Use them at your own discretion and risk.