feat: initial app template catalog with 16 apps

Populate the appstore-apptemplates repo with catalog.json and
per-app config files for all 16 curated Docker apps, each at v1.0.0.

apps/mariadb/app.json

@@ -0,0 +1,10 @@
+{
+  "id": "mariadb",
+  "name": "MariaDB",
+  "description": "Community-developed relational database forked from MySQL",
+  "category": "Databases",
+  "iconName": "mariadb",
+  "latestVersion": "1.0.0",
+  "versions": ["1.0.0"],
+  "maintainer": "serve.zone"
+}