[docker exporter] Support non-service packages

[HT154]

Docker containers aren't just used for running services; they're frequently used to package tools (eg. the Habitat studio) and more. The docker exporter should support these use cases as well. Support should be added for:

• Packaging non-service packages with no entrypoint at all (i.e. to make base images for [docker exporter] Support building images FROM exported "base images" #5589)
• User-provided entrypoints (i.e. for one-shot processes), like @elliott-davis's https://github.com/chuckleheads/pkg-export-oci

[jtimberman]

Example use case:

I have a repository that has several scripts that are run as cron jobs to pull data out of various API services and toss that data into a database, or an S3 bucket, or other such purposes. I can export the docker container with hab pkg export docker and then use it in a kubernetes cronjob resource like this:

---
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: ingest-logs
  namespace: cron-package
spec:
  schedule: "0 0 * * *"
  jobTemplate:
    spec:
      template:
        spec:
          imagePullSecrets:
            - name: registry-secret
          containers:
          - name: cron-package
            image: jtimberman/cron-package:acceptance
            command:
              - /bin/bash
            args:
              - -c
              - /bin/ingest-logs.sh
            env:
              some env stuff, etc

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. We value your input and contribution. Please leave a comment if this issue still affects you.

[HT154]

Don't close this. The fact that issues like this haven't been addressed is one of the primary reasons my org is moving away from all use of Habitat. The use of the stale bot just adds insult to injury.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. We value your input and contribution. Please leave a comment if this issue still affects you.

[stale]

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