Update Scheduler Pallet Documentation (#14740)

* Update pallet scheduler documentation, warning section, guidelines update

* Update call filter note

Co-authored-by: Kelvin Bonilla <bonilla_kelvin@hotmail.com>

* revert format cargo

* Doc wording

Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

* Doc wording

Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

* Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

Ammend comments related to documentation

* Include additional warning section in `on_initialize` hook

* Amend doc

Co-authored-by: Sam Johnson <sam@durosoft.com>

* Amend doc

Co-authored-by: Sam Johnson <sam@durosoft.com>

* Move no_std to appropriate place

* Amend doc

Co-authored-by: Nate Armstrong <naterarmstrong@gmail.com>

* Amend comment

Co-authored-by: Nate Armstrong <naterarmstrong@gmail.com>

---------

Co-authored-by: Kelvin Bonilla <bonilla_kelvin@hotmail.com>
Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>
Co-authored-by: Sam Johnson <sam@durosoft.com>
Co-authored-by: Nate Armstrong <naterarmstrong@gmail.com>

substrate/frame/support/src/traits/hooks.rs

@@ -270,9 +270,14 @@ pub trait Hooks<BlockNumber> {
 	/// Must return the non-negotiable weight of both itself and whatever [`Hooks::on_finalize`]
 	/// wishes to consume.
 	///
+	/// ## Warning
+	///
 	/// The weight returned by this is treated as `DispatchClass::Mandatory`, meaning that
 	/// it MUST BE EXECUTED. If this is not the case, consider using [`Hooks::on_idle`] instead.
 	///
+	/// Try to keep any arbitrary execution __deterministic__ and within __minimal__ time
+	/// complexity. For example, do not execute any unbounded iterations.
+	///
 	/// NOTE: This function is called BEFORE ANY extrinsic in a block is applied, including inherent
 	/// extrinsics. Hence for instance, if you runtime includes `pallet-timestamp`, the `timestamp`
 	/// is not yet up to date at this point.