Add the information about Stoplight Spectral linter support for "codequality" reports
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Stoplight Spectral is a popular OpenAPI linter that supports code-climate format for its reports.
It would be helpful to see it in the list of supported tools in https://docs.gitlab.com/ci/testing/code_quality/.
See also:
- https://github.com/stoplightio/spectral/issues/2283
- https://github.com/stoplightio/spectral/tree/develop/packages/formatters
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