Plugin interfaces interact poorly with multiple IPFS nodes

Specifically:

* Passing the config & repo on `Init` is probably _not_ the right way to go as init needs to be called globally.
* `PluginDaemon.Start()` should return an `io.Closer` handle so multiple daemons can run in a single process.

Start by tracing the plugin Init path and PluginDaemon.Start() interface in the Kubo source. Review how config and repo are passed and how daemon lifetime is managed. Done means the plugin interfaces support global initialization and multiple daemons in one process, with the intended close behavior defined and covered by tests.

Written by the indexing model from the issue text.