[Task] Unify the different `Delete` methods

[Himangini]

Description

See comment here

• (7~ methods) Tasks for creating/deleting stacks (returning a *tasks.TaskTree) e.g.NewTasksToCreateIAMServiceAccounts, NewTasksToDeleteIAMServiceAccounts, DeleteTasksForDeprecatedStacks
• (4~ methods) Deleting stacks directly (not via task), e.g. DeleteStackSync(s *Stack) error, DeleteStackBySpec(s *Stack) (*Stack, error)

We need to

• Unify the different Delete methods (@Skarlso might of tried this recently?) into 1 func that has a DeleteOpts that allow you to customise how the deletion works (via spec/name, sync/async)

[github-actions]

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