Extend .payments() call builder to encompass add'l non-payment types

[Shaptic]

As described by the docs, the /payments endpoint returns a collection of operations rather than, specifically, the Payment Operation:

Operations that can be returned by this endpoint include: create_account, payment, path_payment_strict_recieve, path_payment_strict_send, and account_merge.

This PR expands the types to the PaymentCallBuilder accordingly.

Note that this is a breaking change, because anyone using this call builder will now need to either cast the returned records or handle all of the variations.

[github-actions]

Size Change: +859 B (0%)

Total Size: 12.1 MB

Filename	Size	Change
dist/stellar-sdk.js	6.96 MB	+455 B (0%)
dist/stellar-sdk.min.js	5.1 MB	+404 B (0%)

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