In an effort to improve performance and overall reliability, this PR moves the responsibility of uploading the Pulumi program from the Pulumi Service to the CLI. (Part of fixing https://github.com/pulumi/pulumi-service/issues/313.)
Previously the CLI would send (the dozens of MiB) program archive to the Service, which would then upload the data to S3. Now the CLI sends the data to S3 directly, avoiding the unnecessary copying of data around.
The Service-side API changes are in https://github.com/pulumi/pulumi-service/pull/323. I tested previews, updates, and destroys running the service and PPC on localhost.
The PR refactors how we handle the three kinds of program updates, and just unifies them into a single method. This makes the diff look crazy, but the code should be much simpler. I'm not sure what to do about supporting all the engine options for the Cloud-variants of Pulumi commands; I suspect that's something that should be handled at a later time.
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