[loki-distributed] memberlist not enabled in indexGateway despite indexGateway.joinMemberlist defaults to "true"

[Skaronator]

I noticed missing configuration for the indexGateway.

The helm-chart enables, by default, indexGateway.joinMemberlist: true which means that the Deployment is configured in a way to work with the memberlist. But this is not reflected in the Loki configuration.

By default, memberlist is not enabled for the indexGateway since index_gateway.mode: simple.

helm-charts/charts/loki-distributed/values.yaml

Lines 1610 to 1611 in 8a725bc

	# -- Whether the index gateway should join the memberlist hashring
	joinMemberlist: true

https://grafana.com/docs/loki/latest/configure/#index_gateway

So I'd suggest that indexGateway.joinMemberlist should default to false since it looks like, that this is only important in a multi tenant usecase. (which is by default also disabled)

I'd also suggest that correctly configuring index_gateway.mode and index_gateway.ring once indexGateway.joinMemberlist: true.