f64 support for distribution metric type

[mbellani]

Thanks for adding distribution metric type support to cadence. It looks like the value types supported for distribution are only u64. There are cases however where distribution can be reported in fractions and it would be really great to either add that interface or change the type from u64 to f64. DataDog's datagram format does support both float and an integer, we currently use it this way in a custom metric type that we created. Also happy to open a PR if you like.

Thanks for all your work this library.

[56quarters]

A PR that mirrors the way f64 was added for gauges would be great if you can, thanks!

[56quarters]

Actually @mbellani, I've got some changes that I've been meaning to put up for a PR that will make the value for each metric call generic and remove the need for suffixed methods like _duration and _f64. Do you have an immediate need for an f64 distribution type? If not, I'd rather not have you waste the work for something that's going to be deprecated imminently.

[mbellani]

@56quarters that sounds good to me, I'm not in a hurry, we currently have an implementation of Distribution metric that works pretty well and happy to switch whenever a more generic type support is added. I think generic type support would be great 👍🏽