Add privileged flag, allow adding absolute path for volume

[ferranbt]

#186

We used it in our own components in our fork, especially for the case when binding paths which are not in the project path ~/.playground/devnet (like i.e. /var/run/docker.sock).
It is not being used in the standard builder-playground but we thought it might be useful to have it there for projects which fork the builder-playground and add their own components to it, like we did.
But I also understand if it's not desired to keep it upstream. Feel free to either close or approve.