Make threshold configurable for TreeOverlay #230

Job	Run time
Check (libp2p)	3m 16s
Rust lints (libp2p)	4m 21s
Check (waku)	6m 0s
Test Suite (libp2p, ubuntu-latest)	8m 1s
Rust lints (waku)	5m 14s
Test Suite (libp2p, windows-latest)	14m 35s
Test Suite (libp2p, macos-latest)	11m 55s
Test Suite (waku, ubuntu-latest)	11m 48s
Test Suite (waku, windows-latest)	18m 49s
Test Suite (waku, macos-latest)	13m 55s
	1h 37m 54s

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