Deprecate derived_quantities, traps, exports etc

[RemDelaporteMathurin]

Following #697 and other similar PRs we now have classes like DerivedQuantities, Traps etc inheriting from list.

We kept attributes like derived_quantities, traps, exports etc for backwards compatibility but it is time to remove them.

Example:

FESTIM/festim/exports/derived_quantities/derived_quantities.py

Lines 66 to 72 in 21591ed

	@property
	def derived_quantities(self):
	warnings.warn(
	"The derived_quantities attribute will be deprecated in a future release, please use festim.DerivedQuantities as a list instead",
	DeprecationWarning,
	)
	return self