fix(ad_insights): exclude marketing_messages_website_purchase_values field

[ebnermic]

Summary

• Adds marketing_messages_website_purchase_values to EXCLUDED_FIELDS in ad_insights.py
• Field is rejected by the Facebook Ads Insights API with error code #100: marketing_messages_website_purchase_values is not valid for fields param
• Follows the same pattern as other already-excluded marketing_messages_* fields

Test plan

• Run tap-facebook with an account that previously triggered the error
• Confirm sync completes without #100 API error on ad_insights stream

🤖 Generated with Claude Code

[ebnermic]

Hi @edgarrmondragon,

Would it be possible to get a review on this?
Our pipeline is currently failing due to this, otherwise we would need to work with the fork which would be a bit of a shame.

Thank a lot!