Consider parameterise the `era_payout` formula

[gpestana]

Currently, the era_payout implementation has a few hardcoded parameters that affect the overall inflation and era rewards. Thus, a runtime upgrade is required to update any of those paramsters, e.g. when adjusting the ideal stake rate as explained here.

Consider parameterise the era_payout formula by moving some of the params to storage and gate them by governance.

Todo:

• set ideal_stake (perquintill) through governance, instead of using the number of parachain slots to calculate
• set max_annual_inflation (perquintill) through governance
• set min_annual_inflation (perquintill) through governance
• set falloff (perquintill) through governance
• set max_staking_rewards (perquintill) through governance Implements maximum validator payout per era #1859
• all values should default to the current ones

Consider using the already available parameters pallet and move the MaxStakedRewards and all inflation-related configs there as well.

[Polkadot-Forum]

This issue has been mentioned on Polkadot Forum. There might be relevant details there:

https://forum.polkadot.network/t/adjusting-polkadots-ideal-staking-rate-calculation/3897/11

[gpestana]

Perhaps the best way forward is to expose ideal staking rate to governance and make it independent of the number of parachains.

related: https://forum.polkadot.network/t/adjusting-polkadots-ideal-staking-rate-calculation/3897/23?u=gpestana

[kianenigma]

once parameters pallet is audited, we should proceed with adding it to the relay runtimes and using it for this.

#2061