Rename confidential note references to internal notes

What does this MR do and why?

With copy changes made in !87403 (merged), there are still a lot of places within frontend that refer to internal notes as confidential in our codebase, this MR attempts to clean up those, of course, we'd still need API to be updated first so that all pending reference can be refactored.

Screenshots or screen recordings

NA

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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Related to #363801 (closed)