Issue #18716 Add REST API Discovery Doc and List generator functions to db.

### Get a Discovery List:

    SELECT xt.js_init();

    select xt.dispatch($${"username": "admin",
            "requestType":"dispatch",
            "className": "XT.Discovery",
            "functionName":"getList",
            "isJSON": true,
            "parameters": [null, "https://mobile.xtuple.com/"]
    }$$);

### Get a Discovery Document for Contact. Use null instead to get all.

    SELECT xt.js_init();

    select xt.dispatch($${"username": "admin",
            "requestType":"dispatch",
            "className": "XT.Discovery",
            "functionName":"getDiscovery",
            "isJSON": true,
            "parameters": ["Contact", "https://mobile.xtuple.com/"]
    }$$);