made cssh also work with ssh config host ids

eg
```sh
cssh monitoring.tunnel
```
fixes [https://bugzilla.ipr.univ-rennes.fr/show_bug.cgi?id=4405]

home/bin/cssh

@@ -1,11 +1,13 @@
 #!/usr/bin/env python3
 import logging
-from typing import Optional, List
+from typing import Optional, List, Dict
 import argparse
 import re
 import subprocess
 import abc
 import atexit
+from pathlib import Path
+import os
 
 
 class RgbColor():
@@ -354,16 +356,118 @@ def get_host_real_fqdn(host_id: HostId) -> HostId:
     assert is_valid_host_fqdn(host_real_fqdn), f'invalid host name: {host_real_fqdn}'
     return host_real_fqdn
 
+class SshHostConfig():    
+    '''
+    Host flique-macpro6.tunnel
+        hostname flique-macpro6.ipr.univ-rennes1.fr
+        user francois
+        ProxyCommand ssh graffy@tunnel1.ipr.univ-rennes1.fr nc %h %p 2> /dev/null
+
+    Host physix-frontal.ipr.univ-rennes1.fr
+        hostname physix-frontal.ipr.univ-rennes1.fr
+        user graffy
+        IdentityFile ~/.ssh/homekey
+        
+    Host gpgpu
+        hostname physix58.ipr.univ-rennes1.fr
+        ProxyCommand ssh -i ~/.ssh/homekey graffy@physix.ipr.univ-rennes1.fr nc %h %p 2> /dev/null
+        IdentityFile ~/.ssh/homekey
+
+    Host gpu-p100
+            hostname physix90.ipr.univ-rennes1.fr
+            ProxyCommand ssh -i ~/.ssh/homekey graffy@physix.ipr.univ-rennes1.fr nc %h %p 2> /dev/null
+            IdentityFile ~/.ssh/homekey
+
+    Host cloud.tunnel
+            hostname cloud.ipr.univ-rennes.fr
+            ProxyCommand ssh graffy@tunnel1.ipr.univ-rennes.fr nc %h %p 2> /dev/null
+
+    Host adminpod-1.tunnel
+            hostname adminpod-1.ipr.univ-rennes.fr
+            ProxyCommand ssh graffy@tunnel1.ipr.univ-rennes1.fr nc %h %p 2> /dev/null
+
+    Host mazinger.tunnel
+            hostname mazinger.ipr.univ-rennes.fr
+            ProxyCommand ssh graffy@tunnel1.ipr.univ-rennes1.fr nc %h %p 2> /dev/null
+
+    # git.ipr.univ-rennes.fr
+    Host vmipr-p1 git
+            hostname vmipr-p1.univ-rennes.fr
+            User graffy
+            IdentityFile ~/.ssh/id_ed25519
+    '''
+    names: List[SshHostConfigId]  # eg ['vmipr-p1', 'git']
+    attrs: Dict[SshHostConfigAttr, str]  # eg {'hostname': 'vmipr-p1.univ-rennes.fr', 'User': 'graffy', 'IdentityFile': '~/.ssh/id_ed25519'}
+
+    def __init__(self):
+        self.names = []
+        self.attrs = {}
+        
+
+class SshConfig():
+
+    host_configs = List[SshHostConfig]
+
+    def __init__(self):
+        self.host_configs = []
+
+    def get_host_name(self, host_config_id) -> Optional[str]:
+        host_name = None
+        for host_conf in self.host_configs:
+            if host_config_id in host_conf.names:
+                host_name = host_conf.attrs['hostname']
+                break
+        return host_name
+    
+
+def parse_ssh_config(ssh_config_file_path) -> SshConfig:
+    ssh_config = SshConfig()
+    with open(ssh_config_file_path, 'rt', encoding='utf8') as f:
+        for line in f.readlines():
+            logging.debug('line = %s', line)
+
+            # skip comments
+            if re.match(r'^\s*#.*$', line):
+                continue
+
+            match = re.match(r'^\s*(?P<attr_name>[^\s]+)\s+(?P<attr_value>.*)$', line)
+            if match:
+                # Host vmipr-p1 git
+                # hostname vmipr-p1.univ-rennes.fr
+                # User graffy
+                # IdentityFile ~/.ssh/id_ed25519
+                attr_name = match['attr_name'].lower()
+                attr_value = match['attr_value']
+                logging.debug('attr_name = %s', attr_name)
+
+                if attr_name == 'host':
+                    host_config_ids = attr_value.split(' ')             
+                    ssh_config.host_configs.append(SshHostConfig())
+                    ssh_config.host_configs[-1].names = host_config_ids
+                else:
+                    ssh_config.host_configs[-1].attrs[attr_name] = attr_value
+                continue
+    return ssh_config
+
 
 def main():
-    logging.basicConfig(level=logging.INFO)
+    logging.basicConfig(level=logging.DEBUG)
     arg_parser = argparse.ArgumentParser('cssh (colored ssh) opens a terminal window with a background color that depends on the fully qualified domain name of the target machine')
     arg_parser.add_argument('ssh_target', help='eg root@alambix50.ipr.univ-rennes.fr')
     args = arg_parser.parse_args()
     logging.debug(args)
     ssh_target = SshTarget(args.ssh_target)  # eg 'root@alambix50.ipr.univ-rennes.fr'
     
-    ssh_target.host_id = get_host_real_fqdn(ssh_target.host_id)
+    ssh_config_file_path: Path = Path(os.getenv('HOME')) / '.ssh' / 'config'
+    host_real_name = ssh_target.host_id
+    if ssh_config_file_path.exists():
+        ssh_config = parse_ssh_config(ssh_config_file_path)
+        hn = ssh_config.get_host_name(ssh_target.host_id)
+        if hn:
+            host_real_name = hn
+
+    logging.debug('host_real_name = %s', host_real_name)
+    ssh_target.host_id = get_host_real_fqdn(host_real_name)
     logging.debug('ssh_target.host_id = %s', ssh_target.host_id)
     # AS_ROOT='false'
     # if [ "$(echo $@ | grep '^root@' > /dev/null)" ]