Move apps-related templates to applications dir and add yggdrasil template and helpers.

templates/applications/mysql/generic/README.md

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+# MySQL generic metrics
+
+This directory contains a very comprehensive template which will monitor generic MySQL/MariaDB metrics. All available parameters are set.
+
+## Prerequisites
+
+You should have nxagent [configured to use one or more MySQL/MariaDB databases](https://www.netxms.org/documentation/adminguide/database-monitoring.html#mysql).
+
+## Thresholds
+
+This templates uses some defaults thresholds:
+
+* Connection pool usage: (2) >= 90%
+* Maximum connection pool usage: (2) >= 90%
+* Open file pool usage: (2) >= 90%
+* Temporary tables created on disk: (2) >= 50%