Allow variable substitution on data-param-* attributes

## Describe the new feature or change to an existing feature you'd like to see

Since data-param-* attributes will be added as a query parameter for URLs, would be nice to allow variable substitution for them when they are added as query params.

## Additional context

I ran into this need when adding embed_config attribute for amp-youtube, I need to include a value stored in an AMP variable, something like this:

```

```

And the variable is not substituted on the parameter of the request, the URL keeps literally "${ampVariableName}"

```
https://www.youtube.com/get_video_info?html5=1&video_id=i3LHatq2u4k&embed_config={"adsConfig":{"adTagParameters":{"rdp":"${ampVariableName}"}}}
```