[Issue]: Broken machine learning links

[colleenmcginnis]

Type of issue

Missing information

What documentation page is affected

https://www.elastic.co/docs/explore-analyze/machine-learning/data-frame-analytics/ml-feature-processors

What happened?

The links at the bottom of Feature processors are broken:

• Frequency encoding
• Multi encoding
• n-gram encoding
• One hot encoding
• Target mean encoding

It looks like this content is available in the 8.18 docs. Should we (1) link back to the 8.18 docs, (2) should this content be moved to the 9.0 docs, or (3) should we remove these links? Something else?

cc @szabosteve

Additional info

No response

[szabosteve]

I moved this content to 9.0 via #1281