Fix example value for max-message-size

[falko]

@npepinpe once told me to use zeebe.client.message.max-message-size=4194304, which sounds like the default value and seems to be in bytes. If we use a too small example value, users may think the value is in megabytes. Obviously, we could also just document the unit but even then 3 bytes is likely not a workable value.

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[github-actions]

👋 🤖 ✅ Looks like the changes were ported across versions, nice job! 🎉

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