ci: Fix release-PR flow

[blukat29]

Proposed changes

• Remove the deprecated darwin executor and packaging-darwin jobs
• Rename to kaia in release_rc.sh
• Rename sample testnet conf to something like kend_kairos.conf.

Types of changes

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• Bugfix
• New feature or enhancement
• Others

Checklist

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• I have read the CONTRIBUTING GUIDELINES doc
• I have read the CLA and signed by comment I have read the CLA Document and I hereby sign the CLA in first time contribute
• Lint and unit tests pass locally with my changes ($ make test)
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Related issues

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Further comments

• Failed job https://app.circleci.com/pipelines/github/kaiachain/kaia/116/workflows/68c6f075-ba4c-4b44-b737-76a4b84e14cb