[ci] Adds repo checks in main branch for batch release

[chunhtai]

This fixes main branch part of https://github.com/flutter/flutter/issues/176433

The work left is adjusting cocoon to also run this check in release branch

The high level view of this pr.

1. Move ci_config.yaml and pending changelog parsing into thir own files and the parsed results are exposed as a getter method in RepositoryPackage so that it can be shared between branch_for_release, repo_package_info_check, and version_check
2. The format error of ci_config.yaml and changelog files are reported in repo_package_info_check. The other 2 assume they are correct formatted and throw directly if they are not.
3. update the version_check to be able to handle batch release package

Pre-Review Checklist

• [ ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [ ] I read the Tree Hygiene page, which explains my responsibilities.
• [ ] I read and followed the relevant style guides and ran the auto-formatter.
• [ ] I signed the CLA.
• [ ] The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• [ ] I linked to at least one issue that this PR fixes in the description above.
• [ ] I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or I have commented below to indicate which version change exemption this PR falls under[^1].
• [ ] I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under[^1].
• [ ] I updated/added any relevant documentation (doc comments with ///).
• [ ] I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under[^1].
• [ ] All existing and new tests are passing.

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