Document the executor

[alecandido]

The Executor is now exposed to the user for scripts, and it is only documented in the section https://qibo.science/qibocal/stable/tutorials/advanced.html#how-to-use-qibocal-as-a-library
(other than the docstrings, which are not intended for end user - for sure not as the only reference).

qibocal/doc/source/tutorials/advanced.rst

Lines 25 to 29 in 6789ac8

	#creare executor
	executor = Executor.create(
	platform=platform,
	output=pathlib.Path("experiment_data")
	)

qibocal/doc/source/tutorials/advanced.rst

Lines 63 to 64 in 6789ac8

	executor.run_protocol(t1_signal, t1_params, ExecutionMode.ACQUIRE)
	executor.run_protocol(t1_signal, t1_params, ExecutionMode.FIT)

and by the examples in the runcards/ folder
https://github.com/qiboteam/qibocal/blob/main/runcards/single_shot.py
https://github.com/qiboteam/qibocal/blob/main/runcards/rx_calibration.py

which are also a bit conflicting, since the docs present the direct .run_protocol() usage, which is not the favored interface for the scripts' user (the docs should be updated, as the automated .run_protocol() invocation was not available at the time the tutorial has been written).

• update existing tutorial

A more in-depth guide about the Executor and its features is certainly needed, going through:

• the basic executor instantiation
• the possible alternatives (explicit vs implicit usage, i.e. qibocal.routines)
• the available protocols to be invoked, and their interface
  • whose complete list is only available in https://github.com/qiboteam/qibocal/blob/main/src/qibocal/protocols/__init__.py
  • maybe we should have an automated list as a separate page (not just under the "API reference" section),
  • with links to the individual protocols pages (for those protocols which have those)
  • cf. Automate protocols' docs #1007
• the further methods available (other than protocols)
• a clarification about its role as an object, and compositions' example (passing an open executor to another Python function)