Resolve "Show the activity filter dropdown in discussion tab only, show all discussions always in changes tab"

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• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
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• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #54206 (closed)