Publishing to Maven Central

It would be good to have _all_ JARs (java-ipfs-http-client and all deps) published to Maven Central. There were already several attempts recorded:
* https://github.com/multiformats/java-multibase/issues/32
* https://github.com/multiformats/java-multihash/issues/24
* (maybe more that I missed?)

For this to happen:
* we need to bring all projects "in shape" for publishing (they must pass [requirements](https://central.sonatype.org/publish/requirements/))
* we need to register namespace with Sonatype, I guess `io.ipfs` (at least package name suggest this)
* we need to assign publishers (who are set up for publishing, with things like GPG keys) to the registered namespace

Are we interested in doing this?

Of course, we can continue to use jitpack.io as secondary publishing service, there is not problem with that.

Start by reviewing the Maven Central publishing requirements linked in the issue and the related java-multibase and java-multihash issues. Determine what is needed for all JARs, the io.ipfs namespace, and publisher credentials; done means the projects meet the requirements and all artifacts are published to Maven Central.

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