Push options are an optional capability of a git server. If they are
listed in the servers capabilities, when the client lists push-options
in it's list of capabilities, then the client sends it's list of push
options followed by a flush-pkt.
So, If we have any declared push options, then we will list it as a
client capability, and send the options.
If the request contains push options but the server has no push
options capability, then error.
6fc6eeb66c removed
`git_transport_smart_proxy_option`, and there was nothing added to
replace it. That made it hard for custom transports / smart
subtransports to know what remote connect options to use (e.g. proxy
options).
This change introduces `git_transport_smart_remote_connect_options` to
replace it.
