[llvm] [Github][CI] Introduce `doc8` to `code-lint-helper.py` (PR #172123)

[via llvm-commits]

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@@ -289,8 +291,59 @@ def _clean_clang_tidy_output(self, output: str) -> str:
         return ""
 
 
+class Doc8LintHelper(LintHelper):
+    name: Final = "doc8"
+    friendly_name: Final = "documentation linter"
 
-ALL_LINTERS = (ClangTidyLintHelper(),)
+    def instructions(self, files_to_lint: Sequence[str], args: LintArgs) -> str:
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EugeneZelenko wrote:

```suggestion
    def instructions(self, files_to_lint: Iterable[str], args: LintArgs) -> str:
```

https://github.com/llvm/llvm-project/pull/172123