feat(source-amazon-ads): Add Sponsored Brands campaign-level report stream with cost/spend metrics

## Feature Request

### Describe the feature request

The Amazon Ads connector currently lacks a Sponsored Brands campaign-level report stream that includes cost/spend metrics. The old V2 `SponsoredBrandsReportStream` included cost data but was removed in v6.0.0 (Oct 2024) due to Amazon deprecating the V2 Reporting API. The V3 replacement (`sponsored_brands_v3_report_stream`) only covers the `sbPurchasedProduct` report type, which does not include cost/spend metrics.

Meanwhile, the Sponsored Display and Sponsored Products families were split into granular campaign-level report streams in v7.0.0 — and those **do** include `cost` (e.g., `sponsored_products_campaigns_report_stream`, `sponsored_display_campaigns_report_stream`). But no equivalent `sponsored_brands_campaigns_report_stream` was created.

This creates a gap where users who previously relied on Sponsored Brands cost data no longer have access to it through the connector.

### Describe the solution you'd like

Add a new `sponsored_brands_campaigns_report_stream` (and `_daily` variant) using the Amazon Ads V3 `sbCampaigns` report type, similar to how `sponsored_products_campaigns_report_stream` and `sponsored_display_campaigns_report_stream` were implemented. This stream should include cost, spend, impressions, clicks, and other campaign-level performance metrics.

### Describe alternatives you've considered

Users could potentially use the `sponsored_brands_campaigns` (non-report) stream for some campaign metadata, but this does not include performance/cost metrics. There is no current workaround for obtaining Sponsored Brands cost data through the Airbyte connector.

### Additional context

- The V2 `SponsoredBrandsReportStream` was removed in v6.0.0 via https://github.com/airbytehq/airbyte/pull/47366
- The V3 migration in v7.0.0 (https://github.com/airbytehq/airbyte/pull/48449) added granular campaign-level streams for Sponsored Display and Sponsored Products but not for Sponsored Brands
- Amazon Ads V3 API supports `sbCampaigns` report type which includes cost metrics: https://advertising.amazon.com/API/docs/en-us/guides/reporting/v3/report-types
- Migration guide: https://docs.airbyte.com/integrations/sources/amazon-ads-migrations

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[Devin session](https://app.devin.ai/sessions/87d8960862224cb8b0b1cf35bc5f5a32)

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**Internal Tracking:** https://github.com/airbytehq/oncall/issues/11541