Querying obsolete products through openfoodfacts-query

[stephanegigandet]

It's possible to get lists of obsolete products by adding ?obsolete=1 to URLs. In that case we issue query on the products_obsolete collection.

e.g. to see brands for which we have products marked obsolete: https://world.openfoodfacts.org/brands?obsolete=1

This behavior does not seem to be implemented with the openfoodfacts-query service.

[john-gom]

I've raised PR #9 on openfoodfacts-query to handle this. Will raise a separate PR on off-server to supply the obsolete tag when this is in the request.
In the same PR I'll remove the code that falls back to product_tags