{Packaging} Add warning message for Azure Linux 2.0 (#31545)

Author: jiasli

src/azure-cli/azure/cli/__main__.py

@@ -9,6 +9,7 @@
 start_time = timeit.default_timer()
 
 import sys
+import os
 
 from azure.cli.core import telemetry
 from azure.cli.core import get_default_cli
@@ -22,6 +23,14 @@
 
 logger = get_logger(__name__)
 
+AZURELINUX2_WARNING_MESSAGE = (
+    "Azure CLI 2.74.0 is the final version available on Azure Linux (Mariner) 2.0 and will not receive further "
+    "updates. "
+    "We recommend migrating to Azure Linux 3.0 to access newer versions of Azure CLI and continue receiving updates. "
+    "For more information: https://go.microsoft.com/fwlink/?linkid=2322402. "
+    "To disable this warning message, set AZURE_CLI_DISABLE_AZURELINUX2_WARNING environment variable to any value. "
+)
+
 
 def cli_main(cli, args):
     return cli.invoke(args)
@@ -96,7 +105,6 @@ def cli_main(cli, args):
                         else:
                             upgrade_exit_code = subprocess.call(cmd, shell=platform.system() == 'Windows')
                     else:
-                        import os
                         devnull = open(os.devnull, 'w')
                         cmd.append('-y')
                         upgrade_exit_code = subprocess.call(cmd, shell=platform.system() == 'Windows', stdout=devnull)
@@ -115,6 +123,9 @@ def cli_main(cli, args):
     except Exception as ex:  # pylint: disable=broad-except
         logger.debug("Intercept survey prompt failed. %s", str(ex))
 
+    if 'AZURE_CLI_DISABLE_AZURELINUX2_WARNING' not in os.environ:
+        logger.warning(AZURELINUX2_WARNING_MESSAGE)
+
     telemetry.set_init_time_elapsed("{:.6f}".format(init_finish_time - start_time))
     telemetry.set_invoke_time_elapsed("{:.6f}".format(invoke_finish_time - init_finish_time))
     telemetry.conclude()