feature: Add version output as cli arg

Fixes: #89

.changelogs/1.0.4/89_add_version_output.yml

@@ -0,0 +1,2 @@
+added:
+  - Add version output cli arg. [#89]

README.md

@@ -198,6 +198,7 @@ The following options and parameters are currently supported:
 | -j | --json | Returns a JSON of the VM movement. | Unset |
 | -b | --best-node | Returns the best next node for a VM/CT placement (useful for further usage with Terraform/Ansible). | Unset |
 | -m | --maintenance | Sets node(s) to maintenance mode & moves workloads away. | Unset |
+| -v | --version | Returns the ProxLB version on stdout. | Unset |
 
 ### Balancing
 #### General

proxlb

@@ -209,9 +209,17 @@ def initialize_args():
     argparser.add_argument('-j', '--json',        help='Return a JSON of the VM movement.',                     action='store_true', required=False)
     argparser.add_argument('-b', '--best-node',   help='Returns the best next node.',                           action='store_true', required=False)
     argparser.add_argument('-m', '--maintenance', help='Sets node to maintenance mode & moves workloads away.', type=str,            required=False)
+    argparser.add_argument('-v', '--version',     help='Returns the current ProxLB version.',                   action='store_true', required=False)
     return argparser.parse_args()
 
 
+def proxlb_output_version():
+    """ Print ProxLB version information on CLI. """
+    print(f'{__appname__} version {__version__}\nRequired config version: >= {__config_version__}')
+    print('ProxLB support: https://github.com/gyptazy/ProxLB\nDeveloper: gyptazy.com')
+    sys.exit(0)
+
+
 def initialize_config_path(app_args):
     """ Initialize path to ProxLB config file. """
     info_prefix  = 'Info: [config]:'
@@ -1495,6 +1503,8 @@ def main():
     # Initialize PAS.
     initialize_logger('CRITICAL')
     app_args = initialize_args()
+    if app_args.version:
+        proxlb_output_version()
     config_path = initialize_config_path(app_args)
     pre_validations(config_path)