Add missing subscription fields

[dgalambos]

AutoResumeDate, GracePeriodExpiresDate, RefundedAt, OwnershipType, and StoreTransactionID fields are missing from the Subscriptions struct fields. This PR adds them to the struct.
To maintain consistency, OwnershipType is its own type, as official documentation is (similar to PeriodType):

ownership_type | string
Enum: "PURCHASED" "FAMILY_SHARED"
How the Customer received access to this subscription:
* PURCHASED: The Customer purchased the product.
* FAMILY_SHARED: The Customer has access to the product via their family.

StoreTransactionID is not documented by RevenueCat, but is part of the response sent.

Also - minor typo fixed in Store comment. This could have been its own PR, but for a tiny single-word change in a comment, I figured it could be merged together.

[dgalambos]

Ping @mhemmings