router deployments - start supporting --private flag

[qrkourier]

Add a bootstrapping var ZITI_ROUTER_PRIVATE which sends ziti create config router edge --private when "true"

[dovholuknf]

What if we simply allow a string to be supplied that's added to the config comand instead so that people can override more than just this?

[qrkourier]

Like ZITI_BOOTSTRAP_CONFIG_ARGS?