Add support for injecting configuration data into the transform definitions

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Currently integration configuration data, for example [`interval`](https://github.com/elastic/integrations/blob/main/packages/qualys_vmdr/data_stream/asset_host_detection/manifest.yml#L15), cannot be injected into the transform definition, confirmed [here](https://github.com/elastic/package-spec/issues/833#issuecomment-3249402300).

Making the transform retention user-configurable is often asked before, for example [here](https://github.com/elastic/enhancements/issues/26303). Some integrations have a workaround by injecting variables into input config, then into the ingest pipeline, and then into the transform through a field. This workaround is less efficient. It would be nice to control it better by directly injecting the configuration data into the transforms. Also a direct option to control the transform would have a better user experience as well.

By allowing user configuration data injected into the transform, users can control the transform retention efficiently.

Example: Based on [`interval`](https://github.com/elastic/integrations/blob/main/packages/qualys_vmdr/data_stream/asset_host_detection/manifest.yml#L15-L20) value,

```yaml
retention_policy:
time:
field: "@timestamp"
max_age: {{ interval }}
```

Start with the referenced packages/qualys_vmdr/data_stream/asset_host_detection/manifest.yml example and review the linked package-spec discussion. Trace how integration configuration currently reaches transform definitions and determine the required design. Done means users can inject configuration such as interval directly into a transform so it controls retention without the input-to-pipeline workaround.

Written by the indexing model from the issue text.