Because the Pulumi.yaml file demarcates the boundary used when
uploading a program to the Pulumi.com service at the moment, we
have trouble when a Pulumi program uses "up and over" references.
For instance, our customer wants to build a Dockerfile located
in some relative path, such as `../../elsewhere/`.
To support this, we will allow the Pulumi.yaml file to live
somewhere other than the main Pulumi entrypoint. For example,
it can live at the root of the repo, while the Pulumi program
lives in, say, `infra/`:
Pulumi.yaml:
name: as-before
main: infra/
This fixespulumi/pulumi#575. Further work can be done here to
provide even more flexibility; see pulumi/pulumi#574.
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