[feature] e2e tests for container generator workflow

[ianlewis]

trafficstars

• [x] Different triggers (push, workflow_dispatch, schedule, new-tag)
  • [x] push
    • https://github.com/slsa-framework/example-package/pull/93
  • [x] schedule
    • https://github.com/slsa-framework/example-package/pull/91
  • [x] workflow_dispatch
    • https://github.com/slsa-framework/example-package/pull/94
  • [x] tag
    • https://github.com/slsa-framework/example-package/pull/95
• [ ] Different branches (for each trigger above)
  • [ ] push
  • [ ] schedule
  • [ ] workflow_dispatch
  • [ ] tag
• [x] ~~Pre-submit e2e tests~~ (pre-submits can't be done because of permissions issues for pull_request targets)
  • #637
• [ ] Different arguments: vary the env variables, make sure the final provenance contains the right information
• [ ] Builder information, such as runner env (except hash)

[ianlewis]

Assigned to @asraa based on past discussion.

[ianlewis]

Added e2e tests for the generic container workflow.