Kusama v0.7.21

Release focussed on stability and footprint. This should sort out many of the chronic performance issues of the previous two releases.

Native for runtime 1049.

Core changes

• Use jmalloc, align kvdb crate version. (#883)
• Update yamux to version 0.4.4. (#868)
• Update to libp2p 0.16.2 (#867)

Runtime changes

• Separate WeightToFee calculation for Kusama and Polkadot (#854)
• Force ED to not be zero (#838)
• Enable migrations in polkadot and kusama runtimes (#824)

Runtime changes (Substrate)

• Introduce default-setting prime for collective (paritytech/substrate#5137)
• Introduce on_runtime_upgrade (paritytech/substrate#5058)
• Adds vested_transfer to Vesting pallet (paritytech/substrate#5029)

Substrate changes

• Use 128mb for db cache default (paritytech/substrate#5134)
• Introduce Prometheus metric endpoint replacing Grafana endpoint (paritytech/substrate#4981)
• Add more metrics to prometheus (paritytech/substrate#5034)
• Open one substream for each notifications protocol (paritytech/substrate#4909)
• Build block without checking signatures (paritytech/substrate#4916)
• Adds fork-awareness and finalization notifications to transaction pool watchers. (paritytech/substrate#4740)
• Subsystems memory tracking: 1. Transaction pool (paritytech/substrate#4822)
• CLI improvements & fixes (paritytech/substrate#4812)
• Added GetCallMetadata for extrinsic calls. (paritytech/substrate#4791)