Adding api call to get bundle page using product slug

[rnbr04]

The current implementation of the wrapper can get product's page data using EpicGamesStoreAPI.get_product().

However, sometimes a free offer may contain a bundle, whose data can only be fetched via
https://store-content.ak.epicgames.com/api/en-US/content/bundles/{slug}.

Creating a PR for the same.