config: Catch missing Bridge for ClientTransportPlugin

First of all, tor doesn't support multiple transport name on a single *TransportPlugin line so get rid of that. The manpage has never documented that feature and it complexifies the line for no reason. A user can just use multiple ClientTransportPlugin line instead.

Second, if no Bridge line is found, error immediately and exit. Don't leave the Bridge line alone there leading to bugs like #25528 (closed)

Third, when making sure we have a Bridge line with a ClientTransportPlugin, we now check at the managed proxy list. In order to pull this off, the transport name had to be added to the managed_proxy_t object so we can match for which transport it is used for. And thus justifying the removal of multiple transport support which adds no benefit except complexity.

Fixes #40106 (closed)

Signed-off-by: David Goulet dgoulet@torproject.org