feat(dcgw): REP security group and troubleshooting content

[cloudjumpercat]

Description

Fixes #4213

Preview Links

• /dedicated-cloud-gateways/aws-resource-endpoints/#configure-vpc-security-group-inbound-rules
  • Note: This can't be tested since it's highly dependent on how the customer chooses to configure their backend, so this is more of a reference/guidance than an end-to-end flow.
• /dedicated-cloud-gateways/aws-resource-endpoints/#troubleshooting-timeouts

Checklist

• Tested how-to docs. If not, note why here.
• All pages contain metadata.
• Any new docs link to existing docs.
• All autogenerated instructions render correctly (API, decK, Konnect, Kong Manager).
• Style guide (capitalized gateway entities, placeholder URLs) implemented correctly.
• Every page has a description entry in frontmatter.
• Add new pages to the product documentation index (if applicable).

[netlify]

✅ Deploy Preview for kongdeveloper ready!

Name	Link
🔨 Latest commit	6c4872b
🔍 Latest deploy log	https://app.netlify.com/projects/kongdeveloper/deploys/6a340588bb99860008dca4a9
😎 Deploy Preview	https://deploy-preview-5603--kongdeveloper.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
🤖 Make changes	Run an agent on this branch

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[Copilot]

Pull request overview

This PR updates the Dedicated Cloud Gateways AWS Resource Endpoints how-to to document AWS VPC Lattice security group nuances and provide timeout troubleshooting guidance, addressing issue #4213.

Changes:

• Added guidance on configuring VPC security group inbound rules using the VPC Lattice managed prefix list.
• Added a troubleshooting section for request timeouts / missing NLB traffic.
• (Needs follow-up) Keep the how-to ending with a validation step and fix a broken validation curl command.