Dec 4 (Reuters) - Amazon's investments in new fulfillment centers and delivery stations have gradually cemented the online giant's position ​as a key player in the nearly $193 billion U.S. ‌parcel industry, long dominated by UPS, FedEx, and the U.S. Postal Service. The company said ‌on Thursday it was in discussions with the U.S. Postal Service about the relationship and was considering its options before the current contract expires next year. Here's a snapshot of the U.S. delivery market: * The ⁠U.S. ...