Update agent/common-problems.md (#1920)

Cross-link [Agent
diag](https://www.elastic.co/docs/troubleshoot/ingest/fleet/common-problems#trb-collect-agent-diagnostics)
to its [CLI
diag](https://www.elastic.co/docs/reference/fleet/agent-command-reference#elastic-agent-diagnostics-command)
counterpart.

---------

Co-authored-by: Brandon Morelli <[email protected]>

Author: stefnestor

troubleshoot/ingest/fleet/common-problems.md

@@ -362,7 +362,7 @@ The ZIP archive containing diagnostics information will include the raw events o
 
 **Get the diagnostics bundle using the CLI**
 
-Run the following command to generate a zip archive containing diagnostics information that the Elastic team can use for debugging cases.
+Run the [`diagnostics` command](/reference/fleet/agent-command-reference.md#elastic-agent-diagnostics-command) to generate a zip archive containing diagnostics information that the Elastic team can use for debugging cases:
 
 ```shell
 elastic-agent diagnostics