Publish JSON schema to GitHub pages

[JamieMagee]

As far as I can see, the JSON schema is only available at https://raw.githubusercontent.com/ossf/osv-schema/main/validation/schema.json. But raw.githubusercontent.com isn't really designed to be used as a CDN, which means that putting it in a $schema property isn't appropriate.

Copying the schema as part of the GitHub pages deployment, to something like https://ossf.github.io/osv-schema/schema.json, would be better in the long run

[oliverchang]

Thanks for the suggestion! Would you be open to submitting a PR for adding this to https://ossf.github.io/osv-schema/schema.json ?

[JamieMagee]

@oliverchang I created #232