CA-413424: Enhance xe help output

[BengangY]

The previous xe help is as below:

Usage: xe <cmd> [-s server] [-p port] ([-u username] [-pw password] or [-pwf <password file>]) [--traceparent traceparent] <other arguments>

A full list of commands can be obtained by running
	xe help -s <server> -p <port>

The previous xe help output lacked debug-related options and did not provide detailed parameter description.
The new xe help output is as follows:

Usage:
  xe <command>
    [ -s <server> ]            XenServer host
    [ -p <port> ]              XenServer port number
    [ -u <username> -pw <password> | -pwf <password file> ]
                               User authentication (password or file)
    [ --nossl ]                Disable SSL/TLS
    [ --debug ]                Enable debug output
    [ --debug-on-fail ]        Enable debug output only on failure
    [ --traceparent <value> ]  Distributed tracing context
    [ <other arguments> ... ]  Command-specific options

A full list of commands can be obtained by running
  xe help -s <server> -p <port>

[changlei-li]

I would suggest not to keep two duplications of usage text in the code (here and newcli.ml) to avoid extra maintenance effort. For this case, usage appears in xe help and xe help --all. We can fill the usage part in client side(newcli.ml) and the remaining part (command list) in server side (here) and compose them together as the command output.

[lindig]

I would suggest to merge this; it is already an improvement and if there is no appetite for more changes it's good enough.