[protobuf-schema] Replace zero value enum suffix from UNKNOWN to UNSPECIFIED

[lucy66hw]

ref #20472
Based on protobuf style guide The zero value enum should have the suffix UNSPECIFIED.

• Changed protobuf CONFIG OPTIONS from startEnumsWithUnknown to startEnumsWithUnspecified.
• ENUM zero value change to UNSPECIFIED suffix.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• 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 Git BASH)
  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.
• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request. @wing328

[reta]

@lucy66hw just a question please, reading the https://protobuf.dev/best-practices/dos-donts/#unspecified-enum. it seems like the right name for first element should have UNSPECIFIED suffix, fe <enum_name>_UNSPECIFIED. Shouldn't we follow this convention? Thank you.

[lucy66hw]

@reta thanks for comment. yes, this is the target of the PR. It replaces the current zero enum suffix from UNKNOWN to UNSPECIFIED. The enum_name prefix will be added by function addEnumValuesPrefix, resulting in the zero enum being named <enum_name>_UNSPECIFIED

[reta]

@wing328 wondering if you could find a time to look into this small change, thank you

[amberzsy]

@wing328 could you look into this pr?

[wing328]

thanks for the PR, which has been merged

pushed 61ae569 to update the doc