Consider making output of `List` from `Keystore` interface streamable/chunked

[ilyaigpetrov]

The current declaration of Keystore's List() ([]string, error) doesn't take any arguments and returns the whole list of keys per one output. I suggest making it a line-buffered stream.

boxo/keystore/keystore.go

Lines 31 to 32 in c9cb61d

	// List returns a list of key identifier
	List() ([]string, error)

My use case comes from ipfs/kubo#11102 (comment):

Currently the key listing accumulates all the keys and outputs them to terminal in one write.
I think, it would be better to output line-buffered stream of keys to the terminal.
It's related because the case is the same: generating keys in batches.