Test if changing default codec to JSON would work

[oruebel]

Motivation

See #285 The goal is to see if JSON codec works with the types that we need to support.

• Change default codec in ZarrIO to JSON
• Remove the object_codec_class option from NWBZarrIO

Checklist

• Did you update CHANGELOG.md with your changes?
• Does the PR clearly describe the problem and the solution?
• Have you reviewed our Contributing Guide?
• Does the PR use "Fix #XXX" notation to tell GitHub to close the relevant issue numbered XXX when the PR is merged?