wanfed via mesh gateways in secondary datacenters should use gateways on startup if configured

[rboyer]

After #7931, startup of a secondary server will always dial the primary datacenter's mesh gateways directly, because the feedback loop gets a positive "safe to use local mesh gateways" signal from the federation state replicator, but in establishLeadership that hasn't started yet.

We could change this so that if there ARE federation states recorded in the state store, we should use those on startup, and only switch back to dialing direct if we get 3 failures in a row (similar to what we do outside of just startup to fix connectivity issues).

Affects 1.8+

[rboyer]

One thing that will have to be done is to use the existence of replicated FederationState data as a signal to override the serf "fs" feature flag.

[rboyer]

There may be a similar interaction with the "are acls upgraded" serf feature flag that slows down convergence after full secondary dc restarts.