[REQUEST]: Update Agentless FAQ document

[smriti0321]

Description

We do not support Agentless integrations in case customer has traffic filtering in their cluster. We should add a new FAQ to handle this.

Resources

https://www.elastic.co/guide/en/serverless/current/agentless-integration-troubleshooting.html

Which documentation set does this change impact?

Elastic Cloud (Hosted and Serverless) only

Feature differences

No diff

What release is this request related to?

N/A

Collaboration model

The documentation team

Point of contact.

Main contact: @benironside

Stakeholders: @smriti0321 @orestisfl @olegsu