In FCV_AND_FEATURE_FLAG_README.md, we document how to add feature-specific upgrade/downgrade code.

However, there are many functions where code can be added. For example for upgrade we have:

• _shardServerPhase1Tasks
• _prepareToUpgradeActions
• _userCollectionsUassertsForUpgrade
• _userCollectionsWorkForUpgrade
• _upgradeServerMetadata
• _finalizeUpgrade

The aim of this ticket is to analyze how we have used those (in master, v8.0, v7.0, etc.) for feature-specific code, and which parameters if any they need from setFCV.

We should also understand if any are unnecessary and/or can be merged. For example, usually it seems that code inside _userCollectionsWorkForUpgrade could be moved to _upgradeServerMetadata but we should figure out if that's true in general.