Add protobuf 3.18.1

[chausner-audeering]

Specify library name and version: protobuf/3.18.1

This adds version 3.18.1 for protobuf. Some applications require very specific versions of protobuf so it's good to have all minor versions of protobuf available on ConanCenter.

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• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.

[CLAassistant]

All committers have signed the CLA.

[ericLemanissierBot]

I detected other pull requests that are modifying protobuf/all recipe:

• - [protobuf] fix clang-cl #10005
• [protofbuf] protobuf versions 3.19.3 and 3.19.4 #9400
• (#8129) Bump version Protobuf 3.17.3 #8130

This message is automatically generated by https://github.com/ericLemanissier/conan-center-conflicting-prs so don't hesitate to report issues/improvements there.

[uilianries]

@chausner-audeering Thank you for your contribution, please, ask for user access on the issue #4, otherwise the CI bot will not validate your PR.

[conan-center-bot]

All green in build 3 (ff06abacd266bee0f9c30d76ea3a6d8cb9858159):

• protobuf/3.18.1@:
  All packages built successfully! (All logs)

[conan-center-bot]

This PR has been automatically merged due Bump version or Bump dependencies label.
Read https://github.com/conan-io/conan-center-index/blob/master/docs/labels.md#bump-version to obtain more information.