add MariaDB to installation doc (#5247)

as discussed in #5237

doc/02-Installation.md

@@ -36,6 +36,7 @@ thoroughly.
   monitor your infrastructure
 * A web server, e.g. Apache or Nginx
 * PHP version ≥ 7.2
+* MariaDB
 
 ### Optional Requirements
 
@@ -401,9 +402,9 @@ You will need to install certain dependencies depending on your setup:
 * The [pdfexport](https://github.com/Icinga/icingaweb2-module-pdfexport) module (≥0.10) is required for the
   export to PDF
 * LDAP PHP library when using Active Directory or LDAP for authentication
-* MySQL or PostgreSQL PHP libraries
+* MariaDB/MySQL or PostgreSQL PHP libraries
 
-The following example installs Apache2 as web server, MySQL as RDBMS and uses the PHP adapter for MySQL.
+The following example installs Apache2 as web server, MariaDB as RDBMS and uses the PHP adapter for MariaDB/MySQL.
 Adopt the package requirements to your needs (e.g. adding ldap for authentication) and distribution.
 
 Example for RHEL/CentOS/Fedora:

doc/05-Authentication.md

@@ -1,6 +1,6 @@
 # Authentication <a id="authentication"></a>
 
-You can authenticate against Active Directory, LDAP, a MySQL or a PostgreSQL database or delegate
+You can authenticate against Active Directory, LDAP, a MariaDB, MySQL or PostgreSQL database or delegate
 authentication to the web server.
 
 Authentication methods can be chained to set up fallback authentication methods
@@ -136,7 +136,7 @@ resource = my_ad
 
 ## Database Authentication <a id="authentication-configuration-db-authentication"></a>
 
-If you want to authenticate against a MySQL or a PostgreSQL database, you have to define a
+If you want to authenticate against a MariaDB, MySQL or PostgreSQL database, you have to define a
 [database resource](04-Resources.md#resources-configuration-database) which will be referenced as data source for the database
 authentication method.
 
@@ -289,5 +289,5 @@ asks that backend to authenticate the user with the sAMAccountName "jdoe".
 ### SQL Database <a id="domain-aware-auth-sqldb"></a>
 
 When the user "[email protected]" logs in, Icinga Web 2 walks through all configured authentication backends until it
-finds one which is responsible for that user -- e.g. a MySQL backend (SQL database backends aren't domain-aware). Then
+finds one which is responsible for that user -- e.g. a MariaDB or MySQL backend (SQL database backends aren't domain-aware). Then
 Icinga Web 2 asks that backend to authenticate the user with the username "[email protected]".

doc/07-Preferences.md

@@ -3,7 +3,7 @@
 Preferences are settings a user can set for their account only,
 for example the language and time zone.
 
-Preferences can be stored either in a MySQL or in a PostgreSQL database. The database must be configured.
+Preferences can be stored either in a MariaDB, MySQL or in a PostgreSQL database. The database must be configured.
 
 ## Configuration <a id="preferences-configuration"></a>