Use keyword and not parameter in CI docs

What does this MR do?

As per the related issue, we are mixing keyword and parameter when talking about YAML config. After looking through our docs and details about YAML, it's clear that we need to use keyword as the standard word for the configuration words in GitLab CI/CD config files. It's already the most common word we use, we just need to replace the remaining cases of parameter, but only when it applies to GitLab CI/CD keywords.

Related issues

Related to #244621 (closed)

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