Adds option for http agent for user in slack callback (#9836)

* Adds option for http agent for user in slack callback

* Adds changelog fragment for 9836 issue

* Apply suggestions from code review

Co-authored-by: Felix Fontein <felix@fontein.de>

* Fix typo.

---------

Co-authored-by: Abhijeet Kasurde <akasurde@redhat.com>
Co-authored-by: Felix Fontein <felix@fontein.de>

changelogs/fragments/9836-option-for-http-agent-for-user-to-callback-slack.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - slack callback plugin - add ``http_agent`` option to enable the user to set a custom user agent for slack callback plugin (https://github.com/ansible-collections/community.general/issues/9813, https://github.com/ansible-collections/community.general/pull/9836).

plugins/callback/slack.py

@@ -18,6 +18,11 @@ short_description: Sends play events to a Slack channel
 description:
   - This is an ansible callback plugin that sends status updates to a Slack channel during playbook execution.
 options:
+  http_agent:
+    description:
+      - HTTP user agent to use for requests to Slack.
+    type: string
+    version_added: "10.5.0"
   webhook_url:
     required: true
     description: Slack Webhook URL.
@@ -106,7 +111,7 @@ class CallbackModule(CallbackBase):
         self.username = self.get_option('username')
         self.show_invocation = (self._display.verbosity > 1)
         self.validate_certs = self.get_option('validate_certs')
-
+        self.http_agent = self.get_option('http_agent')
         if self.webhook_url is None:
             self.disabled = True
             self._display.warning('Slack Webhook URL was not provided. The '
@@ -132,8 +137,13 @@ class CallbackModule(CallbackBase):
         self._display.debug(data)
         self._display.debug(self.webhook_url)
         try:
-            response = open_url(self.webhook_url, data=data, validate_certs=self.validate_certs,
-                                headers=headers)
+            response = open_url(
+                self.webhook_url,
+                data=data,
+                validate_certs=self.validate_certs,
+                headers=headers,
+                http_agent=self.http_agent,
+            )
             return response.read()
         except Exception as e:
             self._display.warning(f'Could not submit message to Slack: {e}')