fix(aigw): Policy examples add display_name

[cloudjumpercat]

Description

Fixes #6810

Preview Links

As I was testing these, I ran into several more errors unreleated to display_name, so I fixed those as well.
I've tested all the changed examples with 1.13.0 kongctl and Konnect API.

• /ai-gateway/policies/opentelemetry/#custom-attributes-by-lua (ripped this one out of the include because there were too many differences after fixing them, also I commented out a section that was in the original include because it's unclear if they use the same logging table now, I've asked here)
• /ai-gateway/policies/loggly/#custom-fields-by-lua
• /ai-gateway/policies/file-log/#custom-fields-by-lua
• /ai-gateway/policies/http-log/#custom-fields-by-lua
• /ai-gateway/policies/pre-function/
• /ai-gateway/policies/ai-rate-limiting-advanced/
• /ai-gateway/policies/ai-prompt-template/ (another one that had an error outside of the scope of display_name that I've fixed)
• /ai-gateway/policies/ai-prompt-guard/

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).

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