need Peers Count api

[thienpow]

the api lack of Peers Count

because pooling for peers count by getting a full list of peers is not making sense,

const peerInfos = await ipfs.swarm.peers({ timeout: 2500 })
return peerInfos.length

especially when the peers is around 6k-7k list... every 2.5s pooling for the long list is consuming CPU inefficiently.

Originally posted by @thienpow in #7528 (comment)

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[anthonybudd]

I agree this would be a helpful feature.

A simple workaround when using the cli is:
ipfs swarm peers | wc -l