Make timeout tries configurable on command line

The max number of allowed timeouts is [hardcoded to 1](https://github.com/99designs/cmdstalk/blob/fbd704da919d283643e673bd02efcf0221224b92/broker/broker.go#L26). It would be nice if that was configurable through a command line flag.

The hardcoded timeout tries constant is in broker/broker.go line 26. Look at how other command-line flags are defined and parsed in the codebase, likely in a main.go or similar entry point. Add a new flag for max timeouts, pass it to the broker, and update the constant usage. Test by running the broker with the new flag.

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