feat(bling): add rpmfusion install script

[xynydev]

After the upstream change with ublue switching to negativo, adding rpmfusion seems to have become a common thing people try to do, and also a common cause of issues.

We should make a script that can:

• Install rpmfusion properly
• Disable conflicting repos (negativo?)
• Detect if rpmfusion is already installed but disabled (and enable it)
• what else?

[fiftydinar]

@qoijjj Tagging you, as you also expressed interest in this