Showtech sonic mgmt framework: Add Management Framework functionality for "show tech-support" (#7816)

Provide the changes required for supporting the "show-techsupport" command via the SONiC Management Framework front end mechanisms (CLI, REST, and gNOI). The Management Framework functionality implemented by this PR improves on the the capabilities currently provided by the SONiC Click CLI interface via the "show techsupport" command by providing the following additional features:

- User-friendly "help" information describing command syntax details for CLI invocation.
- Ability to invoke the command via REST and gNOI mechanisms.

Unit test results are attached to this PR.

src/sonic-host-services/host_modules/showtech.py

@@ -0,0 +1,50 @@
+"""Show techsupport command handler"""
+
+import host_service
+import subprocess
+import re
+
+MOD_NAME = 'showtech'
+
+class Showtech(host_service.HostModule):
+    """DBus endpoint that executes the "show techsupport" command
+    """
+    @host_service.method(host_service.bus_name(MOD_NAME), in_signature='s', out_signature='is')
+    def info(self, date):
+
+        ERROR_TAR_FAILED = 5
+        ERROR_PROCFS_SAVE_FAILED = 6
+        ERROR_INVALID_ARGUMENT = 10
+
+        err_dict = {ERROR_INVALID_ARGUMENT: 'Invalid input: Incorrect DateTime format',
+                    ERROR_TAR_FAILED: 'Failure saving information into compressed output file',
+                    ERROR_PROCFS_SAVE_FAILED: 'Saving of process information failed'}
+
+        cmd = ['/usr/local/bin/generate_dump']
+        if date:
+            cmd.append("-s")
+            cmd.append(date)
+
+        try:
+            result = subprocess.run(cmd, capture_output=True, text=True,
+                                    check=True)
+
+        except subprocess.CalledProcessError as err:
+            errmsg = err_dict.get(err.returncode)
+
+            if errmsg is None:
+                output = 'Error: Failure code {:-5}'.format(err.returncode)
+            else:
+                output = errmsg
+
+            print("%Error: Host side: Failed: " + str(err.returncode))
+            return err.returncode, output
+
+        output_file_match = re.search('\/var\/.*dump.*\.gz', result.stdout)
+        output_filename = output_file_match.group()
+        return result.returncode, output_filename
+
+def register():
+    """Return the class name"""
+    return Showtech, MOD_NAME
+