command: Minimal integration of new provider installer in "init"
command: Minimal integration of new provider installer in "init"

There's still a lot of work to do here around both the UX and the
follow-up steps that need to happen after installation completes, but this
is enough to faciliate some initial end-to-end testing of the new-style
install process.

heimweh/terraform,VladRassokhin/terraform,tommynsong/terraform,apparentlymart/terraform,rnaveiras/terraform,ewbankkit/terraform,ewbankkit/terraform,pryorda/terraform,apparentlymart/terraform,rnaveiras/terraform,pdecat/terraform,hashicorp/terraform,heimweh/terraform,VladRassokhin/terraform,tommynsong/terraform,tommynsong/terraform,pdecat/terraform,pdecat/terraform,apparentlymart/terraform,apparentlymart/terraform,apparentlymart/terraform,pdecat/terraform,pryorda/terraform,heimweh/terraform,pryorda/terraform,heimweh/terraform,VladRassokhin/terraform,ewbankkit/terraform,heimweh/terraform,hashicorp/terraform,rnaveiras/terraform,ewbankkit/terraform,VladRassokhin/terraform,hashicorp/terraform