Add information about running on controller

[janisz]

In the current implementation, running a scan on an Agent poses several challenges:

• Backward Compatibility: Enforcing Agent-based scans creates compatibility issues since Agents may not always be configured to connect to ACS (External Service).
• Serialization: We must ensure data is serialized to facilitate the transfer from an Agent to the Controller, allowing presentation of results to the user.
• Testing Complexity: Extending our end-to-end testing with an additional Controller/Agent setup is required to adequately test Agent functionality. However, this introduces complexity into our testing process.

In light of these challenges, it is more practical to run scans on the Controller rather than the Agent.

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Refs: https://issues.jenkins.io/browse/JENKINS-71622
Closes:

• JENKINS-71169: run on agent #270