Update Docs to correct Price Object

[advra]

The documentation here shows the following:

pricing.tcgplayer.updated Number ✅
pricing.tcgplayer.unit Number ✅
pricing.cardmarket.updated Number ✅
pricing.cardmarket.unit Number ✅

Correct to the correct types:

pricing.tcgplayer.updated String ✅
pricing.tcgplayer.unit String ✅
pricing.cardmarket.updated String ✅
pricing.cardmarket.unit String ✅

Also include missing ProductIds for tcgplayer/cardmarket. For example querying https://api.tcgdex.net/v2/en/cards/base1-2 results in a pricing that has idProduct/productId which are not documented. This fix includes these.

pricing.cardmarket.idProduct
pricing.tcgplayer.productId

[advra]

Will address this in MR (will link here)

Edit: #234