ref: use version of statsdproxy that can work with Duration

[Litarnus]

This PR uses a fixed commit for statsdproxy that takes a Duration instead of u64 seconds as flush_interval so we can see if reducing the flush_interval helps with the metrics problem.

This is meant as a proof of concept, if it works we will update the statsdproxy crate to support it regulary.

statsdproxy PR: getsentry/statsdproxy#55

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