fix: AI Gateway metrics info

[cloudjumpercat]

Description

Fixes the following:

• Make the Logging label OSS instead of Enterprise
• Add Konnect Advanced Analytics bullet to the AI observability section and label
• Mention AI gateway metrics on Prometheus plugin page and label as Enterprise: This is mentioned in the existing page, it's just referenced later down the page and the customer couldn't find it. I moved it to the "available metrics" section as well with a link to the other section for findability.

https://kongstrong.slack.com/archives/CDSTDSG9J/p1734333985135819

Testing instructions

Preview link:

• https://deploy-preview-8285--kongdocs.netlify.app/gateway/latest/ai-gateway/#konnect-advanced-analytics
• https://deploy-preview-8285--kongdocs.netlify.app/hub/kong-inc/prometheus/#available-metrics

Checklist

• Review label added
• Conditional version tags added, if applicable.

[netlify]

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