feat: add webhook integration test

[abc3]

About

Initial implementation for #1359 that validates transaction consistency through webhook events. The system performs multiple row updates in a table, generating update events that are received and validated for correct sequencing via webhooks.

Running Tests

JEPSEN_TRANSACTIONS_COUNT="100" mix test --only jepsen

Environment Variables

Variable	Default	Description
JEPSEN_HTTP_HOST	"127.0.0.1"	HTTP server host
JEPSEN_HTTP_PORT	"4040"	HTTP server port
JEPSEN_TRANSACTIONS_COUNT	20	Number of transactions to run
JEPSEN_TRANSACTION_QUERIES_COUNT	10	Number of queries per transaction

[fazzone]

Looking good! One thing I am curious about - maybe it's not worth it - what do you think about listening on port 0 and asking the socket what port you got assigned by the OS? The HTTP endpoint can be created in setup with a nonsense port and then there would be a step in the test which does a genserver call to ask for the real port and updates the endpoint accordingly. Or, the creation of the endpoint&sink could be done in a helper function rather than setup and be "private" to the individual test

[abc3]

@fazzone This is a great suggestion, but I'm concerned it might be overengineering. It might be easier to handle this through some env var if more flexibility is needed