Make threshold configurable for TreeOverlay #253

Job	Run time
Rust lints (libp2p)	3m 27s
Check (libp2p)	2m 46s
Rust lints (waku)	5m 34s
Check (waku)	5m 50s
Test Suite (libp2p, ubuntu-latest)	10m 1s
Test Suite (libp2p, windows-latest)	19m 52s
Test Suite (libp2p, macos-latest)	12m 50s
Test Suite (waku, ubuntu-latest)	9m 25s
Test Suite (waku, windows-latest)	16m 10s
Test Suite (waku, macos-latest)	15m 50s
	1h 41m 45s

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