Init-sync: enable peer scorer by default

[farazdagi]

What type of PR is this?

Other / Feature Release

What does this PR do? Why is it needed?

• Peer scorer in init-sync was enabled in --dev for months, so relatively it is much more stable than peer scoring in p2p and/or gossip (which are protected by the very same --enable-peer-scorer flag).
• The purpose of peer scorer in init-sync was to probabilistically select peers that provide better data: if data provided by peer moves head forward well (on average), peer's score gets increased, and peer gets better chances to get selected.
• The problem with ineffective peers was amplified on altona when some clients returned 1 block (or few blocks), and sync was becoming really slow. With peer scorer such ineffective peers can still be selected, but with lesser chances (weighted random selection).
• After discussing with @nisdas we decided to release this part of peer scorer separately, w/o waiting for other types or scoring (to make sure that init sync process is more effective). Since scorers are quite cohesive, and can be used independently, we do not have to couple init-sync scorer's release cycle and that of other types of scoring. It is ready, and has been tested running for long time in --dev mode.

Which issues(s) does this PR fix?

N/A

Other notes for review