[block-input-refactor] handle PARENT_UNKNOWN in gossip handler

[twoeths]

Describe the bug

resolve this TODO

lodestar/packages/beacon-node/src/network/processor/gossipHandlers.ts

Line 185 in d10c4b8

// TODO(fulu): should this be unknownParent event?

Expected behavior

in #8200 when validating a gossip block and got PARENT_UNKNOWN, gossip handler should throw PARENT_UNKNOWN event so that BlockInputSync can search for it
need to check with unstable also

Steps to reproduce

No response

Additional context

No response

Operating system

Linux

Lodestar version or commit hash

mkeil/refactor-block-input-on-unstable