Added new default free tier

refs https://github.com/TryGhost/Team/issues/1037

Free tier is now setup the same way as other tiers, to allow custom description/benefits. This change:

- adds a migration to add a default free tier for all sites
- adds a default fixture to insert a free tier for all new sites

core/server/data/migrations/versions/4.33/2022-01-14-11-51-add-default-free-tier.js

@@ -0,0 +1,37 @@
+const {createTransactionalMigration} = require('../../utils');
+const ObjectID = require('bson-objectid');
+const {slugify} = require('@tryghost/string');
+const logging = require('@tryghost/logging');
+
+module.exports = createTransactionalMigration(
+    async function up(knex) {
+        const [result] = await knex
+            .count('id', {as: 'total'})
+            .from('products')
+            .where('type', 'free');
+
+        if (result.total !== 0) {
+            logging.warn(`Not adding default free tier, a free tier already exists`);
+            return;
+        }
+
+        const name = 'Free';
+        const id = ObjectID().toHexString();
+
+        logging.info(`Adding tier "${name}"`);
+        await knex('products')
+            .insert({
+                id: id,
+                name: name,
+                type: 'free',
+                slug: slugify(id),
+                created_at: knex.raw(`CURRENT_TIMESTAMP`)
+            });
+    },
+    async function down(knex) {
+        logging.info('Removing free tier');
+        await knex('products')
+            .where('type', 'free')
+            .del();
+    }
+);

core/server/data/schema/fixtures/fixtures.json

@@ -3,9 +3,15 @@
         {
             "name": "Product",
             "entries": [
+                {
+                    "name":             "Free",
+                    "slug":             "free",
+                    "type":             "free"
+                },
                 {
                     "name":             "Default Product",
-                    "slug":             "default-product"
+                    "slug":             "default-product",
+                    "type":             "paid"
                 }
             ]
         },