BuildStep doesn't run commands when --skip-preview is used

[wimoMisterX]

The BuildStep pulumi module doesn't run the cmd when --skip-preview is passed to pulumi.

Unfortunately pulumi doesn't expose whether --skip-preview has been used. I've check the process.env and process.argv as well to see if we can determine if --skip-preview is used, and we can't :(

I have 2 solutions in mind:

1. Run the pulumi command with an env variable called PULUMI_SKIP_PREVIEW and that could checked in our BuildStep component.
2. Change the BuildStep into a DynamicResourceProvider and always run the command in the diff method

[JakeGinnivan]

BuildStep needs to move the run into the apply stage.

Either we build outside of the pulumi process (which the NX pulumi plugin can do), or it only builds in plan and not preview.