Metadata validator for validating resource metadata encoded in a page against a registered schema class

[newgene]

Is your feature request related to a problem? Please describe.
A new feature allows validating resource metadata against a registered schema class (if JSON-schema definition exists)

Describe the solution you'd like
A new UI interface like /metadata/validator allows users to validate a copy/pasted JSON metadata or a URL of a page (metadata JSON can then be extracted) against a selected schema class registered in DDE

Describe alternatives you've considered
NA

Additional context
Possible UI ideas from these relevant pages:

• https://validator.schema.org/
• https://www.jsonschemavalidator.net/

And we should consider creating a new backend API endpoint to handle the actual validation, that way it will display the consistent error messages from the metadata input form (the "metadata guide"). The validation functionality might have already existed in the biothings_schema Python package.

[newgene]

For the starting point, we can just allow copy/paste in a JSON object. Extracting from a given page at a URL can be added later, assuming there is a package for it already.

[flaneuse]

a potentially cool variation: does my schema match against any schema within the DDE? Related to the idea of having a discovery.biothings.io/translate to convert between schemas according to mapping schemas defined by @gtsueng