add mariadb and redis links to appcat (#208)

* add mariadb and redis links to appcat

Author: arska

docs/modules/ROOT/nav.adoc

@@ -63,6 +63,8 @@
 
 * Databases
 ** xref:how-to/install-postgres-db-helm.adoc[PostgreSQL]
+** xref:how-to/install-mariadb.adoc[MariaDB]
+** xref:how-to/install-redis.adoc[Redis]
 
 * Migrating from APPUiO Public
 ** xref:tutorials/migration.adoc[Tutorial]

docs/modules/ROOT/pages/how-to/install-mariadb.adoc

@@ -0,0 +1,3 @@
+= Install MariaDB on {product}
+
+Do you want a managed MariaDB that includes Backups, Monitoring, Updates, and optionally 24x7 Support? Check out the https://products.vshn.ch/appcat/mariadb.html[MariaDB by VSHN product description^] and https://docs.appcat.ch/vshn-managed/mariadb/create.html[technical documentation including how to instantiate on {product}^].

docs/modules/ROOT/pages/how-to/install-redis.adoc

@@ -0,0 +1,3 @@
+= Install Redis on {product}
+
+Do you want a managed Redis that includes Backups, Monitoring, Updates, and optionally 24x7 Support? Check out the https://products.vshn.ch/appcat/redis.html[MariaDB by VSHN product description^] and https://docs.appcat.ch/vshn-managed/redis/create.html[technical documentation including how to instantiate on {product}^].