S2 merging exclude sparse peaklets

[dachengx]

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What does the code in this PR do / what does it improve?

Depends on #1494.

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• Update the docstring(s)
• Update the documentation
• Tests to check the (new) code is working as desired.
• Does it solve one of the open issues on github?

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• Until the automated tests pass, please mark the PR as a draft.
• On the XENONnT fork we test with database access, on private forks there is no database access for security considerations.

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[coveralls]

coverage: 89.539% (+0.05%) from 89.488%
when pulling 5ac47f5 on merged_s2s_avg_pos
into 7138149 on master.