Enforce clean startup when importing from snapshot

[fridrik01]

When starting Lotus from snapshot its easy to forget to manually cleanup the .lotus/datastore folder before running the --import-snapshot command. This may result in issues/errors that are difficult to debug.

Proposal

We should check whether the .lotus/datastore folder exists when starting lotus --import-snapshot. If the folder exists, we should do one of:

1. Always exit Lotus with a non-zero exit code and error message that user needs to delete the .lotus/datastore and run the import again.
2. Always automatically cleanup the .lotus/datastore and continue the import.
3. Always ask user (Y/N) whether Lotus should cleanup the .lotus/datastore folder and then (if Y) continue the import, or (if N) exit Lotus with non-zero exit code. Also introduce a --force-import-cleanup flag that if set will automatically select Y so this could be run non-interactively from a script.

Discussion

a) Which (1,2,3) is the best
b) Its my understanding that .lotus/datastore is the only folder that needs to be deleted. However if we will be doing a cleanup of the .lotus/datastore should we also delete other folders like .lotus/sqlite although its not required .
c) For context, this task started from this slack thread.

[rjan90]

I think this can be closed now, as #11032 has been merged. The PR introduces a remove-existing-chain flag which can be used when importing a snapshot to clean up the existing chain data (both splitstore and non-splitstore node) before importing the snapshot. Like this:

lotus daemon --import-snapshot /home/3005040_2023_07_04T08_00_00Z.car.zst --remove-existing-chain=true --halt-after-import

[jennijuju]

from @fridrik01

I think that flag does not address the concern that I raised in 10875, unless we update all our docs to call out that users should always use this flag. But I think we should just make the remove-existing-chain be the default behavior when importing a snapshot and maybe add something like --preserve-existing-chain for those rare cases (if any) where someone wants to keep that data around

I think it would make sense to have a remove-existing-chain = true by default when importing from a snapshot, cuz folks who do so are mostly looking for a fresh chain state or a lighter weight node.

[rjan90]

Closing now that the remove-existing-chain=true is true by default when importing from a snapshot: #11277, which has been merged.