Add server streaming message receive and send histograms

[kuroneko25]

Similar to #71 but for server metrics.

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[kuroneko25]

@googlebot I signed it!

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We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
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[kuroneko25]

@googlebot I fixed it.

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[bwplotka]

Hi 👋🏽

Sorry for the massive, lag. We consolidating projects and moving to single repo where we have more control and awareness. We are moving this code base longer to https://github.com/grpc-ecosystem/go-grpc-middleware/tree/v2 and we moved existing state of Prometheus middleware to https://github.com/grpc-ecosystem/go-grpc-middleware/tree/v2/providers/openmetrics

This means that before we release v2 this is the best opportunity to shape new https://github.com/grpc-ecosystem/go-grpc-middleware/tree/v2/providers/openmetrics with whatever we want to change in API 🤗 If you want to change something effectively long term, I would suggest switching your PR and rebasing it on https://github.com/grpc-ecosystem/go-grpc-middleware/tree/v2/providers/openmetrics instead (notice v2 branch, not master!).

Sorry for the confusion, but it's needed for the project sustainability. Cheers!