Consider a no-setup `pulumi up` process for deploying review stacks

[AaronFriel]

Deploying the Docs site requires running a series of scripts, including creating buckets which are managed outside of Pulumi:

https://github.com/pulumi/docs/blob/85387b0a12e4efe84654722ed37daeaaf0a3c302/scripts/sync-and-test-bucket.sh#L42-L53

To enable building, reviewing, and delivering cross-cutting changes to Docs and other Pulumi surfaces, we should enable building the Docs site via pulumi up in Pulumi Deployments or with minimal state managed outside of Pulumi.

[thoward]

@seanyeh @cnunciato thoughts?