Proposal: License convention

[clbarnes]

I've drafted a proposal for a convention to manage license metadata. https://github.com/clbarnes/zarr-convention-license

tl;dr a license field which is an array of objects, where each object is an externally-tagged enum representation of a license. The variants look like one of:

{"spdx": "CC0-1.0"}
{"url": "https://raw.githubusercontent.com/clbarnes/zarr-convention-license/refs/tags/v1/LICENSE"}
{"text": "This data is licensed under the terms of ..."}
{"file": "relative/path/to/license.txt"}
{"path": "relative/path/to/zarr_node"}  // this zarr node's metadata has license information

[d-v-b]

i think this looks great!