TLS Memberlist

[jtlisi]

Is your feature request related to a problem? Please describe.

Gossip traffic in Cortex using memberlist is not secured on the transport level.

Describe the solution you'd like

We use a custom TCP based transport for our Memberlist client so it should be possible to use a standard set of TLS configs to secure memberlist traffic

Describe alternatives you've considered

UDP based Memberlist implementations trend towards using shared secrets to secure traffic. However, since we use TLS and TLS is used thoughout Cortex, it seems like a secondary system is not worth it.