amp-subscriptions: Render SwG button when "isAccessibleForFree" is "True".

### Description

We would like to use it in free pages as well.
When `"isAccessibleForFree"` is `"True"` in JSON-LD markup, SwG button will not be rendered.

### Alternatives Considered

Navigating users to html page or paywalled page.

### Additional Context

_No response_

Start by locating the amp-subscriptions code that reads JSON-LD markup and decides whether to render the SwG button. Reproduce the case where "isAccessibleForFree" is "True", then verify that the button renders on free pages without changing the existing paywalled behavior.

Written by the indexing model from the issue text.