Update Structure task syntax

[vachillo]

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Describe your changes

Main changes:

• Update Workflow to simplify creation.
• Remove all methods for defining relationships between Tasks directly on a Task.

Context for changes

relevant: #896

currently the two different syntaxes (declarative and imperative) for defining relationships between Tasks for the sake of running them in a Structure (primarily a Workflow). the API for doing so can be confusing because of the many different entrypoints for defining the relationships, and the implementation can be confusing because of the way that the full state of Task relationships are split between Structures and Tasks.

Assumptions made for these changes

• All Structures can generate a graphs of Tasks by calling structure.task_graph. This returns a graph of BaseTask objects.

Issue ticket number and link

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📚 Documentation preview 📚: https://griptape--945.org.readthedocs.build//945/