x/upgrade is an implementation of a Cosmos SDK module that facilitates smoothly
upgrading a live Cosmos chain to a new (breaking) software version. It accomplishes this by
BeginBlocker hook that prevents the blockchain state machine from
proceeding once a pre-defined upgrade block height has been reached.
The module does not prescribe anything regarding how governance decides to do an upgrade, but just the mechanism for coordinating the upgrade safely. Without software support for upgrades, upgrading a live chain is risky because all of the validators need to pause their state machines at exactly the same point in the process. If this is not done correctly, there can be state inconsistencies which are hard to recover from.