Switch to timestamps

[gregdhill]

Block production on Kintsugi and Interlay is sometimes unpredictable which impacts several critical components including (but not limited to):

1. Governance (enactment and delays)
2. Escrow (stake-to-vote period)
3. Vesting (lockup period)

This can hinder estimation and coordination efforts since we cannot reliably predict the height at which things will happen. Polkadot will also introduce asynchronous backing (ETA: Q3 2023) which will reduce parachain block times from 12 to 6 seconds. To improve the reliability of the system and reduce the overhead from this upgrade we should switch to timestamps where it makes sense. One consideration for switching is if block production were to stall we may not want some components to expire prematurely (i.e. issue and redeem).