`package-name` is not documented in schemas/config.json?

I needed `package-name` for a go project, which does not have a supported counterpart of `package.json` of Node. It seems to be work, but [schemas/config.json](https://github.com/googleapis/release-please/blob/main/schemas/config.json) does not mention it.

Here is my working release-please-config.json (details redacted):
```json
{
"$schema": "https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json",
"packages": {
"backend": {
"release-type": "go",
"package-name": "my-project-name-backend"
},
"frontend": {
"release-type": "node"
}
}
}
```