Cleanup formatting & error handling in various stripe services

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What's in this PR?

Cleans up formatting and error handling in our StripeService.xService modules

Mostly what's done here is

• replaced some inline comments with actual @doc blocks
• removed all error handling that takes in a specific value type and returns it unchanged
• removed all _ -> {:error, :unhandled} statements, since this basically swallows error information and makes sentry useless for these cases
• added failure -> failure to all else blocks, so sentry can catch and log them at controller level.
• Got rid of vertically aligned formatting in the few modules that use it.