Add vim to default solbuild image

[liontiger23]

For the occasional venture into chroot it would be very helpful (at least for me) to have vim preinstalled in solbuild.

[davidjharder]

Similarly, I use tree when I can't comprehend the layout of the build directory

[ermo]

It might make sense to have solbuild support a config file that lists the additional things that a user might like to install when building/chrooting?

The context here is that solbuild already installs a lot of things and isn't necessarily quick at doing so.

Hence, if individual users are able to customise their additional solbuild buildroot packages (which will essentially be treated as builddeps), then perhaps that might enable solbuild itself to install fewer packages by default (for a small increase in average speed), yet still enable packagers to specify what they enjoy having at their disposal?

And yes, I am hoping that we can do something similar for boulder.

[liontiger23]

Customization of installed packages would be a great solution.