Add support for clusters with a disabled config db

[gm42]

What would you like to be added/changed?

A FoundationDB cluster can be run with the config db disabled (--no-config-db passed to fdbserver processes); however when operator would issue the coordinators command via fdbcli, this is expected to result in a hanging command (for reference, see https://github.com/apple/foundationdb/commit/cd2bbffa4c412c4c1d599d0dc568d3b28fce4d6b and https://github.com/apple/foundationdb/commit/1a33515934a9c9701c120e4dfc1e478538ab8ffe).

The enhancement request is to allow in some way to run clusters with the config db disabled; this originally came up while discussing mitigations for N2_ConnectError to ghost coordinator IPs, see this forum thread.