Description

1. amp-story-shopping-config can either have a script child or a src attribute
   a) Inline is always required
   b) If a src is present it will override inline
   c) If remote fails it should fallback to the inline config
2. Data should be fetched and set in the store service under a new entry called SHOPPING_STATE.
   products should be keyed to shopping state by their product-tag-id value so they can be read without iterating over data. This could follow a similar pattern as the ADD_PANNING_MEDIA_STATE action.
3. amp-story-shopping-tag should subscribe to SHOPPING_STATE and update its text content with the product-title value.

Validation is not part of this PR. Follow up PRs will validate JSON before setting it. I2I