feat(shed): add --db-path and --epoch-file to indexes events subcommands

[rvagg]

Not sure this is worth merging, but I'm parking this here for now so I don't lose it, it's proven quite helpful.

Taking a clone of an existing database (can be done while running with sqlite3 on the command-line pointing to the events.db file and running .clone path/to/new/file), you can then run inspect-events and backfill-events on the cloned file using --db-path, so you extract data from a lotus node and insert in into an isolated db.

--epoch-file lets me run a specific list of epochs in inspect-events so I can double-check epochs I'm trying to fix when the list of particularly long.