Upgrade to pulumi-docker v4

[thomas11]

This was attempted before in #1044 but had to be reverted in #1054 after conversation with @pierskarsenbarg and @lukehoban.

We need to fix the imageName vs repoDigest issue and get to the bottom of the question about env in the first PR.

This will likely be a breaking update, i.e., a new major version, but ideally we can combine it with #1068 in one new version.

[AaronFriel]

I don't believe "env" is required anymore, but it will be a breaking change to remove it.

Docker builds cannot use env vars directly, a user must pass a build arg which is consumed by the Dockerfile "ARG" statement, that can then be declared as the default value of an env var in the build.

The env input however could control DOCKER_HOST, DOCKER_BUILDKIT, etc. These change Docker engine behavior, and they now respect provider or resource inputs.

[mjeffryes]

the latest pinned version of docker is 4.5.0

[pulumi-bot]

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Please fix these problems and try again.