v7.23.0 release

[wing328]

PR checklist

• Read the contribution guidelines.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

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Summary by cubic

Prepare v7.23.0 by bumping 7.23.0-SNAPSHOT to 7.23.0 in root pom.xml, CLI/core, Maven/Gradle/Mill plugins, online module, and examples (incl. Mill version.properties). Also updates the release script to include modules/openapi-generator-mill-plugin/pom.xml for future Mill bumps.

^{Written for commit 9509508. Summary will update on new commits.}