Add plugins option support for TRACE_START and TRACE_LIST

[Noremos]

Add support for the plugin option for user trace session (introduced in the FirebirdSQL/firebird#8707 )

This should solve #55

Examples:

with connect_server('', user='SYSDBA', password='masterkey') as srv:
    trace_session_id = srv.trace.start(config="database\n{\nenabled = true\n}", name="mytrace", plugins=["myplugin","fbtrace"])
    print(trace_session_id)

with connect_server('', user='SYSDBA', password='masterkey') as srv:
    for k,v in srv.trace.sessions.items():
        if v.flags[0] == 'active':
            print(f"Trace {v.name}: Plugins: {v.plugins}")

[Noremos]

@pcisar, I commited the ‎src/test.py file by mistake. Could you remove it?