docs(event-gateway): add record.value.schema.metadata expression fields - #6556

Changed pages include:

• index.html - view
• _explorer/index.html - view
• admin-api/index.html - view
• ai-gateway/index.html - view
• api/index.html - view
• catalog/index.html - view
• changelogs/index.html - view
• contributing/index.html - view
• cookbooks/index.html - view
• custom-dashboards/index.html - view

There are more changes not included in the list