feat(source-bing-ads): Add AssetGroupPerformanceReportRequest support

## Feature Request

**Connector:** source-bing-ads

### Description

The Microsoft Advertising (Bing Ads) API v13 includes an [AssetGroupPerformanceReportRequest](https://learn.microsoft.com/en-us/advertising/reporting-service/assetgroupperformancereportrequest?view=bingads-13) reporting data object that provides performance metrics at the Asset Group level (used in Performance Max campaigns).

This report type is currently not supported by the Airbyte source-bing-ads connector — it is absent from both the built-in report streams and the Custom Reports `reporting_object` enum.

### Requested Streams

Add support for Asset Group Performance Report at the standard aggregation levels:
- `asset_group_performance_report_hourly`
- `asset_group_performance_report_daily`
- `asset_group_performance_report_weekly`
- `asset_group_performance_report_monthly`

### Available Columns (per Microsoft docs)

`TimePeriod`, `AccountName`, `AccountId`, `CampaignName`, `CampaignId`, `AccountStatus`, `CampaignStatus`, `AssetGroupId`, `AssetGroupName`, `AssetGroupStatus`, `Impressions`, `Clicks`, `Ctr`, `Spend`, `AverageCpc`, `Conversions`, `Revenue`, `ReturnOnAdSpend`, `CampaignType`, `CostPerConversion`

### Workaround

There is currently no workaround within the connector, as the Custom Reports feature only allows report objects from a hardcoded enum which does not include `AssetGroupPerformanceReportRequest`.

### References

- Microsoft API docs: https://learn.microsoft.com/en-us/advertising/reporting-service/assetgroupperformancereportrequest?view=bingads-13
- Draft PR with implementation: https://github.com/airbytehq/airbyte/pull/80271

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**Internal Tracking:** https://github.com/airbytehq/oncall/issues/12921