Added plugin based author and public tag models in API v2 (#10284)

refs #10124

- Author model returns only users that have published non-page posts
- Added a public controller for tags (should be extracted to separate Content API controller TryGhost/Ghost#10106)
- Made resource configuration dynamic based on current theme engine
- This needs a follow-up PR with fixes to the problems described in the PR

packages/bookshelf-has-posts/lib/bookshelf-has-posts.js

@@ -0,0 +1,60 @@
+const _ = require('lodash');
+const _debug = require('ghost-ignition').debug._base;
+const debug = _debug('ghost-query');
+
+const addHasPostsWhere = (tableName, config) => {
+    const comparisonField = `${tableName}.id`;
+
+    return function (qb) {
+        return qb.whereIn(comparisonField, function () {
+            const innerQb = this
+                .distinct(`${config.joinTable}.${config.joinTo}`)
+                .select()
+                .from(config.joinTable)
+                .whereRaw(`${config.joinTable}.${config.joinTo} = ${comparisonField}`)
+                .join('posts', 'posts.id', `${config.joinTable}.post_id`)
+                .andWhere('posts.status', '=', 'published');
+
+            debug(`QUERY has posts: ${innerQb.toSQL().sql}`);
+
+            return innerQb;
+        });
+    };
+};
+
+const hasPosts = function hasPosts(Bookshelf) {
+    const modelPrototype = Bookshelf.Model.prototype;
+
+    Bookshelf.Model = Bookshelf.Model.extend({
+        initialize: function () {
+            return modelPrototype.initialize.apply(this, arguments);
+        },
+
+        fetch: function () {
+            if (this.shouldHavePosts) {
+                this.query(addHasPostsWhere(_.result(this, 'tableName'), this.shouldHavePosts));
+            }
+
+            if (_debug.enabled('ghost-query')) {
+                debug('QUERY', this.query().toQuery());
+            }
+
+            return modelPrototype.fetch.apply(this, arguments);
+        },
+
+        fetchAll: function () {
+            if (this.shouldHavePosts) {
+                this.query(addHasPostsWhere(_.result(this, 'tableName'), this.shouldHavePosts));
+            }
+
+            if (_debug.enabled('ghost-query')) {
+                debug('QUERY', this.query().toQuery());
+            }
+
+            return modelPrototype.fetchAll.apply(this, arguments);
+        }
+    });
+};
+
+module.exports = hasPosts;
+module.exports.addHasPostsWhere = addHasPostsWhere;