feat: cmd/ipfs: Make it possible to depend on cmd/ipfs

[magik6k]

Today there are two ways to run kubo with plugins, one on non-linux systems:

• Preload - which requires the plugin to be in the kubo repo, or at least requires manual build of kubo
• Use a Go plugin, which don't work on most systems, and won't work if any build dependency isn't perfectly aligned - which in practice makes them almost completely unusable for anything non-trivial

This PR adds a third way - by depending on cmd/ipfs/kubo it's now possible to depend on this repo to create kubo-derived nodes with user-specified plugins.

I needed this for RIBS, which is a highly-advanced blockstore, that couldn't justifiably "just be integrated" into upstream kubo.

• KuboRIBS main using this functionality: https://github.com/lotus-web3/ribs/blob/a8d8aff2953416bc267debd0ee05f591cca582d9/integrations/kuri/cmd/kuri/main.go#L16-L20
• Which loads this plugin

Review probably easiest commit-by-commit.

[guseggert]

This looks like a much better way to inject plugins than the standard practice of modifying the preloads and rebuilding kubo bin. What are the drawbacks to this?

[BigLep]

@guseggert : maybe this is something you and @magik6k can discuss in person at IPFS Thing 2023?

[BigLep]

2023-05-18 maintainer conversation: all agreed this should get done for the next release. We haven't assigned an owner yet. A doc update should be made to https://github.com/ipfs/kubo/blob/master/docs/customizing.md as well.

[magik6k]

fyi the other branch - https://github.com/ipfs/kubo/compare/magiks-ribs-hacks - is now up to date with master. May make sense to swap this PR to that one

[Stebalien]

Replaced by #10219.