feat: channel field is added to the product_view table

feat: A new message `MarketingMethod` is added
fix!: `destination` field in the `product_performance_view` table is renamed to `marketing_method`
fix!: `destination` term in the `product_view` table is renamed to `reporting_context`
fix!: `predicted_gross_profit_change_fraction` and `predicted_monthly_gross_profit_change` fields are removed from the `price_insights_product_view` table
fix!: `ReportGranularity`, `RelativeDemand`, `RelativeDemandChangeType`, `TrafficSource` enums are wrapped into messages

PiperOrigin-RevId: 573186882

Source-Link: googleapis/googleapis@c88b603

Source-Link: https://github.com/googleapis/googleapis-gen/commit/6ec73a64ed5ad7d1dc7466047279ee7fdd0efcd1
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