Add "consider" field to schema, as weaker alternative to replaced_by

[cmungall]

See https://github.com/OBOFoundry/OBOFoundry.github.io/pull/1724#issuecomment-1010145689

The primary use case is obsolete ontologies, but we could also consider for inactive ones

There is an argument instead have a similar_ontology tag or dynamically derive similar ontologies based on e.g. shared description of domain; this could be used with any ontology regardless of status. But I think this is best considered as a complementary rather than competing proposal

[cthoyt]

How about rdfs:seeAlso, just so it's reusing pre-existing vocabulary?

[cmungall]

that's fine too but much more general. There are some minimal advantages in using a field with a more restricted range in terms of driving what the web page (or use in ontology browsers, if we propagate the metadata back to the ontology) looks like but I have no strong opinions