[Github][CI] Introduce LintHelper class in code-lint-helper.py (llvm#168827)

This commit introduces a new `LintHelper` class to
`llvm/utils/git/code-lint-helper.py`, which lays the groundwork for
integrating additional linters (`doc8`) into Github Action workflow.

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Co-authored-by: EugeneZelenko <[email protected]>

Author: 2 people