Add staged recipe for rpcgen

[anderslindho]

Checklist

• Title of this PR is meaningful: e.g. "Adding my_nifty_package", not "updated recipe".
• Recipe uses the v1 recipe.yaml format, or this PR explains the exceptional requirement for deprecated v0.
• License file is packaged (see the v1 example recipe for an example).
• Source is from official source.
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• Build number is 0.
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[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipes/rpcsvc-proto/recipe.yaml) and found it was in an excellent condition.

[anderslindho]

@conda-forge/help-c-cpp, ready for review!

[simon-ess]

LGTM