Add default buckets for Histogram metric about client_rust

[mxinden]

Correct. Histogram does not implement Default. As you mention above, this is due to not knowing what the buckets should be by default.

[doehyunbaek]

Maybe add default as in client_golang as it is the most popular client implementation?

https://github.com/prometheus/client_golang/blob/66837e3298bdc57a828794c23bacb253ed8c04cd/prometheus/histogram.go#L68

I can contribute a PR as it seems not too hard if you agree.

[hiuwan]

yes, we can refer to the client_golang and client_java to provide default buckets.

[mxinden]

I would rather call this out in the documentation on Histogram, providing an example with the above mentioned default values. I am not in favor of adding a Default implementation that only works for some use-cases, here network latency measurements. I find this confusing for newcomers. Experts will be familiar enough to read the example and thus configure it themselves.

I can contribute a PR as it seems not too hard if you agree.

Improvements to the documentation would be appreciated.

[mxinden]

With #63 merged, I am closing here. Feel free to follow up with further comments.