Load access requests from SSH cert instead of the profile. The profile
only exists on CLI clients, but not in the proxy.
Note: theoretically, SSH cert may be missing in some cases for CLI
clients. We should eventually encode access requests in TLS certs too,
which are always present.
* Added support for connecting API client through tunnel proxy and web proxy addresses (with identity file).
* Added concurrent dialing logic to dial several possible dialing combinations and seamlessly return the first client to connect.
Roman Tkachenko