Cleanup/unordered writes ingester config

[owen-d]

This PR does a few things:

1. Finishes removing the ingester.unordered-writes-enabled config. This has been entirely replaced by the per tenant limit configuration.
2. Always replays WALs with unordered writes enabled. This primarily safeguards against dropping samples due to out_of_order errors when replaying a WAL after moving from unordered_writes: true -> unordered_writes: false. It does this by ensuring all the internals accept unordered writes during WAL replay and switches any differences at the end.
3. Adds a new metric, loki_ingester_limiter_enabled, which reports when it's enabled/disabled. This should help debugging as it overrides some of the embedded overrides, particularly to disable them during WAL replay.

[sandeepsukhani]

LGTM

[owen-d]

ref #1544