Move object reads to `KVStorePersister` post-1417

[TheBlueMatt]

See #1417 (comment)

[johncantrell97]

Happy to continue on this after #1417 goes in. I actually already implemented it in Sensei because it seemed like you didn't want in ldk. I added a read and a list method since read_channelmonitors needs to be able to list all keys/filenames.

Here's what I did, let me know if you think it's roughly what you'd want to add to KVStorePersister for this issue:

https://github.com/L2-Technology/sensei/pull/37/files#diff-af422d8a9ab5e8778884033d55578f060f9d14dde012232f4faeb2b8a49cec92R12

[tnull]

Closing as done in #2472.