[ingesters] Send heartbeat during wall replay

[alanprot]

What this PR does:
We can have ingesters becoming unhealthy during startup if the wall replay takes longer than the heartbeat_timeout.

The reason for that is that the lifecycle service is started only after ingesters open all TSDBs:

cortex/pkg/ingester/ingester.go

Lines 708 to 719 in b855a25

	func (i *Ingester) starting(ctx context.Context) error {
	if err := i.openExistingTSDB(ctx); err != nil {
	// Try to rollback and close opened TSDBs before halting the ingester.
	i.closeAllTSDB()
	return errors.Wrap(err, "opening existing TSDBs")
	}
	// Important: we want to keep lifecycler running until we ask it to stop, so we need to give it independent context
	if err := i.lifecycler.StartAsync(context.Background()); err != nil {
	return errors.Wrap(err, "failed to start lifecycler")
	}

This adds an option on the lifecycle service to configure if the ingester should AutoJoin the ring (flip his state to active).

If the option is set to false, the ingester will only join the ring after the "Join" method is called.

This change allow us to start the lifecycle before executing the wall replay (so the heart will start to beat) but only flip its state to active after all TSDBs are replayed.

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]