The transaction index is now built separately from the main node procedure,
meaning the -txindex flag can be toggled without a full reindex. If digibyted
is run with -txindex on a node that is already partially or fully synced
without one, the transaction index will be built in the background and become
available once caught up. When switching from running -txindex to running
without the flag, the transaction index database will not be deleted
automatically, meaning it could be turned back on at a later time without a full
resync.