feat(firestore-stripe-payments): Update payments collection for refunds

[chetbox]

Resolves #315

Updates the charges property in the payments collection.

Requires adding the charge.refunded webhook handler event.

Screenshots from Firebase Console

Tested by deploying a local copy of the extension in our Firebase test environment.

charges.data[0] property of a payment before refund:

charges.data[0] property of the same payment after refund:

Edit: I realised that a retrieving a Payment Intent does not include the charges list and it's not listed in the Payment Intent object. The charges key does appear in the payments collection, however, so I've updated this change to find and update the Charge object in charges when the charge.refunded data is received.

Edit 2: I formatted the new code with Prettier and removed the package-lock.json changes.