Update installation instructions for easier navigation on icinga.com

[julianbrost]

Slightly different procedure as usual because I missed that #9217 was based on support/2.13 instead of master during the internal review, so we're doing this now the other way around this time to get things into a consistent state again.

This PR is the result of git cherry-pick 659dfc0c528077eda2e0a9400c6f8a710a92c593 with manual conflict resolution in doc/02-installation.md (basically manually applying the changes that happened in that file in the meantime):

git diff v2.13.0..master doc/02-installation.md:

diff --git a/doc/02-installation.md b/doc/02-installation.md
index b6baea00e..4e0462277 100644
--- a/doc/02-installation.md
+++ b/doc/02-installation.md
@@ -151,7 +151,7 @@ CentOS 8 additionally needs the PowerTools repository for EPEL:
 
 ```bash
 dnf install 'dnf-command(config-manager)'
-dnf config-manager --set-enabled PowerTools
+dnf config-manager --set-enabled powertools
 
 dnf install epel-release
 ```
@@ -711,17 +711,20 @@ Set up a MySQL database for Icinga 2:
 # mysql -u root -p
 
 CREATE DATABASE icinga;
-GRANT SELECT, INSERT, UPDATE, DELETE, DROP, CREATE VIEW, INDEX, EXECUTE ON icinga.* TO 'icinga'@'localhost' IDENTIFIED BY 'icinga';
+GRANT ALTER, CREATE, SELECT, INSERT, UPDATE, DELETE, DROP, CREATE VIEW, INDEX, EXECUTE ON icinga.* TO 'icinga'@'localhost' IDENTIFIED BY 'icinga';
 quit
 ```
 
+Please note that the example above uses the very simple password 'icinga' (in `IDENTIFIED BY 'icinga'`). 
+Please choose a better password for your installation.
+
 ![setting up the database on CentOS 7](images/installation/mariadb-centos7.png "Setting up the database on CentOS 7")
 
 After creating the database you can import the Icinga 2 IDO schema using the
-following command. Enter the root password into the prompt when asked.
+following command. Enter the icinga password into the prompt when asked.
 
 ```bash
-mysql -u root -p icinga < /usr/share/icinga2-ido-mysql/schema/mysql.sql
+mysql -u icinga -p icinga < /usr/share/icinga2-ido-mysql/schema/mysql.sql
 ```
 
 #### Enabling the IDO MySQL module <a id="enabling-ido-mysql"></a>

git diff support/2.13..feature/installation-instructions doc/02-installation.md:

diff --git a/doc/02-installation.md b/doc/02-installation.md
index 7483da6c6..004eaf163 100644
--- a/doc/02-installation.md
+++ b/doc/02-installation.md
@@ -624,15 +624,18 @@ Set up a MySQL database for Icinga 2:
 # mysql -u root -p
 
 CREATE DATABASE icinga;
-GRANT SELECT, INSERT, UPDATE, DELETE, DROP, CREATE VIEW, INDEX, EXECUTE ON icinga.* TO 'icinga'@'localhost' IDENTIFIED BY 'icinga';
+GRANT ALTER, CREATE, SELECT, INSERT, UPDATE, DELETE, DROP, CREATE VIEW, INDEX, EXECUTE ON icinga.* TO 'icinga'@'localhost' IDENTIFIED BY 'icinga';
 quit
 ```
 
+Please note that the example above uses the very simple password 'icinga' (in `IDENTIFIED BY 'icinga'`).
+Please choose a better password for your installation.
+
 After creating the database you can import the Icinga 2 IDO schema using the
-following command. Enter the root password into the prompt when asked.
+following command. Enter the icinga password into the prompt when asked.
 
 ```bash
-mysql -u root -p icinga < /usr/share/icinga2-ido-mysql/schema/mysql.sql
+mysql -u icinga -p icinga < /usr/share/icinga2-ido-mysql/schema/mysql.sql
 ```
 
 #### Enable the IDO MySQL feature <a id="enable-ido-mysql"></a>

The capitalization change in powertools was already done somewhere else on support/2.13, so that change was already included.

fixes #9218
forward-port of #9217