[v9] Give type hints to `scope.setSDKProcessingMetadata()`

### Description

Right now the argument passed to `scope.setSDKProcessingMetadata()` is typed as `{ [key: string]: unknown; }`. We would like to be a bit more strict for certain fields on the metadata and type it as 

```ts
interface MetadataOrWhatever {
  request?: RequestEventData;
  [key: string]: unknown;
}
```