Make threshold configurable for TreeOverlay #246

Job	Run time
Check (libp2p)	2m 54s
Test Suite (libp2p, ubuntu-latest)	8m 20s
Check (waku)	4m 29s
Rust lints (libp2p)	3m 3s
Test Suite (libp2p, windows-latest)	23m 45s
Rust lints (waku)	4m 40s
Test Suite (libp2p, macos-latest)	12m 46s
Test Suite (waku, ubuntu-latest)	9m 56s
Test Suite (waku, windows-latest)	26m 46s
Test Suite (waku, macos-latest)	13m 37s
	1h 50m 16s

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