Upgrading Kubo from 0.15 to 0.28

[livid]

There was an IPNS issue starting in version 0.16 that prevented us from upgrading:

https://discuss.ipfs.tech/t/ipfs-name-resolve-does-not-always-return-the-freshest-cid-for-ipns-on-kubo-0-20-0/16624

Now it seems to be fixed, and there is a new feature, ipfs key sign, which could be useful in some new applications:

https://github.com/ipfs/kubo/releases/tag/v0.25.0

So, we began the work to upgrade the bundled Kubo from version 0.15 to the latest, 0.28.

[livid]

I hope this upgrade can fix #338 too.

[kailuo]

Implemented a basic auto migration process in this branch: https://github.com/Planetable/Planet/tree/ipfs-migration, should take care of upgrading existing Kubo binary from version 0.15.0 to 0.28.0 ( repo version 12 -> 15 )