Merge branch '24908-install-instructions-seem-to-have-two-database-steps-out-of-order' into 'master'

Fix documentation to create the `pg_trm` extension before creating the DB

Closes #24908

See merge request !7735

doc/install/installation.md

@@ -175,6 +175,12 @@ We recommend using a PostgreSQL database. For MySQL check the
     ```bash
     sudo -u postgres psql -d template1 -c "CREATE USER git CREATEDB;"
     ```
+    
+1. Create the `pg_trgm` extension (required for GitLab 8.6+):
+
+    ```bash
+    sudo -u postgres psql -d template1 -c "CREATE EXTENSION IF NOT EXISTS pg_trgm;"
+    ```
 
 1. Create the GitLab production database and grant all privileges on database:
 
@@ -182,12 +188,6 @@ We recommend using a PostgreSQL database. For MySQL check the
     sudo -u postgres psql -d template1 -c "CREATE DATABASE gitlabhq_production OWNER git;"
     ```
 
-1. Create the `pg_trgm` extension (required for GitLab 8.6+):
-
-    ```bash
-    sudo -u postgres psql -d template1 -c "CREATE EXTENSION IF NOT EXISTS pg_trgm;"
-    ```
-
 1. Try connecting to the new database with the new user:
 
     ```bash