feat: add getMaxConnections method to connection manager #3837

Job	Run time
Build	3m 4s
Test example js-libp2p-example-browser-pubsub	1m 48s
Test example js-libp2p-example-chat	53s
Test example js-libp2p-example-circuit-relay	53s
Test example js-libp2p-example-connection-encryption	48s
Test example js-libp2p-example-custom-protocols	54s
Test example js-libp2p-example-delegated-routing	1m 52s
Test example js-libp2p-example-discovery-mechanisms	1m 10s
Test example js-libp2p-example-peer-and-content-routing	1m 9s
Test example js-libp2p-example-pnet	54s
Test example js-libp2p-example-protocol-and-stream-muxing	53s
Test example js-libp2p-example-pubsub	57s
Test example js-libp2p-example-transports	52s
Test example js-libp2p-example-webrtc-private-to-private	1m 58s
	18m 5s

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