integration-docs: Rename Jira doc to avoid collision with Jira plugin.

The Jira plugin integration doc will be moved in the next commit, to
"static/generated/integrations/jira/doc.md", as the directory name of
the integration is "jira" in zulip/python-zulip-api.

- Jira integration doc (previously) - "zerver/webhooks/jira/doc.md"
- Jira plugin integration doc (next commit) -
"static/generated/integrations/jira/doc.md"

Both of these will use the same path "jira/doc.md" as their
integration.doc value, and the actual file is loaded based on the order
of template directories listed in computed_settings.py.

Hence, use a custom path for the Jira integration doc to avoid this
collision.

zerver/lib/integrations.py

@@ -510,7 +510,8 @@ WEBHOOK_INTEGRATIONS: list[WebhookIntegration] = [
     ),
     WebhookIntegration("insping", ["monitoring"]),
     WebhookIntegration("intercom", ["customer-support"]),
-    WebhookIntegration("jira", ["project-management"]),
+    # Avoid collision with jira-plugin's doc "jira/doc.md".
+    WebhookIntegration("jira", ["project-management"], doc="jira/jira-doc.md"),
     WebhookIntegration("jotform", ["misc"]),
     WebhookIntegration("json", ["misc"], display_name="JSON formatter"),
     WebhookIntegration("librato", ["monitoring"]),