Improve loadbalancer docs based on SDH

[yetanothertw]

Summary

Fixes #781

To add the recommendation mentioned here I've restructured the page (PREVIEW of changes):

• the port/mode-specific bullets are removed from the unordered list (it's pretty hard to parse the info in the list) and added into a new section in the page Port and mode configuration. The new section includes a table (easier to scan) and replaces the old scattered list items. The table clearly shows that ports 9200/9243 support both HTTP (L7) and TCP (L4) modes, with the corresponding client IP mechanism for each.
• added a new Client IP preservation section to explain the three different mechanisms that can be used to preserve the IP. This way other pages can link to this specific section.
• Updated the prerequisites section in the Manage IP filters in ECE.
• Added links between the two pages (ip filtering and load balancer recommendations).

This will require some Eng Team 👀 to review.

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

Tool(s) and model(s) used: Used Claude 4.6 sonnet to validate some assumptions when building the table.

[github-actions]

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[github-actions]

🔍 Preview links for changed docs

• deploy-manage/deploy/cloud-enterprise/ece-load-balancers.md
• deploy-manage/security/ip-filtering-ece.md

[alstolten]

LGTM