Feature request: Option to install plugins

[deregtd]

Our use case is that we still have .yvmrc files everywhere from when we used yvm (before we moved to mise!). So right now I'm having to use mise-action to install mise, then add a separate mise plugins install -y yarn && mise install after the mise-action step. Would be handy if there was just a plugins list we could add, which mise-action installs before running the mise install step.