feat(infinite-scroll): clarify guidelines

What does this MR do?

This MR clarifies the guidelines for infinite scroll usage.

Does this MR meet the acceptance criteria?

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• The “What does this MR do?” section in the MR description is filled out, explaining the reasons for and scope of the proposed changes, per “Say why not just what”.
  • For example, if the MR is focused on usage guidelines, addressing accessibility challenges could be added in a separate MR.
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• Review requested from any GitLab designer or directly from a maintainer or trainee maintainer.

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