Add delete stack and task scheduling resource

[michieldewilde]

Description of the change

Add delete stack and task scheduling resource.

resource "spacelift_scheduled_task" "task_every" {
  stack_id = spacelift_stack.test.id

  command    = "terraform apply -auto-approve"
  every      = ["*/15 * * * *"]
  timezone   = "UTC"
}

resource "spacelift_scheduled_task" "task_at" {
  stack_id = spacelift_stack.test.id

  command    = "terraform apply -auto-approve"
  at         = "1661943083"
}

resource "spacelift_scheduled_delete_stack" "delete_stack" {
  stack_id = spacelift_stack.test.id

  at               = "1661943083"
  delete_resources = true
}

To import this resource the following id format has to be used ${stack_id}/${scheduling_id}. Where scheduling_id is the last part of the ID of the scheduling config.

Type of change

• [x] New feature (non-breaking change that adds functionality)

Checklists

Development

• [x] Lint rules pass locally
• [x] The code changed/added as part of this pull request has been covered with tests
• [x] All tests related to the changed code pass in development
• [ ] Examples for new resources and data sources have been added
• [ ] Default values have been documented in the description (e.g., "Dummy: (Boolean) Blah blah. Defaults to false.)
• [ ] If the action fails that checks the documentation: Run go generate to make sure the docs are up to date

Code review

• [x] This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• [x] Pull Request is no longer marked as "draft"
• [ ] Reviewers have been assigned
• [ ] Changes have been reviewed by at least one other engineer
• [ ] The target branch is future unless the change is going directly into production

[adamconnelly]

@michieldewilde I've converted this to a draft to avoid us getting notified to review it. Can you mark it as ready again when you're ready to merge it?