Queryables link relation and endpoint issues

[philvarner]

• [Item Search Filter Ext] / : 'http://www.opengis.net/def/rel/ogc/1.0/queryables' (Queryables) link relation missing from both root and each collection
• [Item Search - Filter Ext] Queryables endpoints return Content-Type header 'application/json', must return 'application/schema+json'
• [Item Search - Filter Ext] Queryables endpoint json schmea'$id' value invalid, must be same as queryables url (instead it's the example value given in the Filter Extension)