dag-level, class-level and task-level hooks

[edublancas]

Currently, on_render, on_finish and on_failure hooks can only be set at the task level. making impossible to set the same hook for many tasks at once.

One use case for this is static analysis, an on_render hook could be set for all NotebookRunner tasks to do static analysis in the source code to detect potential issues before executing.

Potential API (similar to how dag.clients work):

from ploomber.tasks import PythonCallable

t = PythonCallable(...)

t.on_render = task_level_on_render
dag.class_on_render[PythonCallable] = class_level_on_render
dag.on_render = dag_level_on_render

[edublancas]

Also take into account that tasks can be executed via an executor or directly using task.build, should dag-level hooks be executed when using task.build?

[edublancas]

class-level hooks discarded. DAG-level hooks already implemetned.