Move Schedule from storage to the Config trait

[athei]

The Schedule is a struct that sees a lot of changes to its fields. The main reason is that every new contract callable function needs a new field. For this reason we made its fields private in #8359. Otherwise we would be burning through major version numbers every time we add a new function. This is not enough, though. Because the Schedule is in storage and also a parameter to the update_schedule dispatchable it is still exposed as a public API.

In order to solve this issue we remove the Schedule from storage and instead make it configurable through the Config type. This will drop the functionality to update the Schedule without a runtime upgrade, though. I argue that this feature wouldn't be that useful because the weight prices are already automatically adjusted depending on chain utilization. Larger changes would need some code changes in most cases. Any objections @pepyakin ?

• Remove the CurrentSchedule item from the pallet.
• Add storage migration which removes it from storage.
• Add the Schedule: Get<Schedule> as an associated type to Config
• Enable debug_println when called via RPC instead of relying on a genesis config as a toggle.
• Make Schedule fields public in order to allow customization.

Making the fields private does not help us with avoiding major version bumps because the public WeightInfo trait still needs to change. We just accept the fact that we will have new major version numbers and expect runtimes to bump the version number and re-run benchmarks. Most of the time that will be everything that is to it.

Partly fixed by #8359 and #8773

[pepyakin]

That makes sense.