Better database connection check

Fixes the MySQL output and adds a rake task to properly check the connection

This will e.g., output something like this

```
Database connection failed with error: FATAL:  Datenbank »bla« existiert nicht
```

lib/tasks/database.rake

@@ -41,7 +41,22 @@ end
 namespace 'openproject' do
   namespace 'db' do
     desc 'Ensure database version compatibility'
-    task ensure_database_compatibility: ['environment', 'db:load_config'] do
+    task check_connection: %w[environment db:load_config] do
+      begin
+        ActiveRecord::Base.establish_connection
+        ActiveRecord::Base.connection.execute "SELECT 1;"
+        unless ActiveRecord::Base.connected?
+          puts "Database connection failed"
+          Kernel.exit 1
+        end
+      rescue StandardError => e
+        puts "Database connection failed with error: #{e}"
+        Kernel.exit 1
+      end
+    end
+
+    desc 'Ensure database version compatibility'
+    task ensure_database_compatibility: %w[openproject:db:check_connection] do
       ##
       # Ensure database server version is compatible
       OpenProject::Database::check!

packaging/scripts/check

@@ -11,10 +11,10 @@ log_ko() {
 }
 
 # try to get a setting to make sure database connection works
-if rake setting:get[protocol] &>/dev/null; then
-  log_ok "MySQL configuration is working"
+if rake openproject:db:check_connection 2>/dev/null; then
+  log_ok "PostgreSQL configuration is working"
 else
-  log_ko "MySQL connection is NOT working"
+  log_ko "PostgreSQL connection is NOT working"
 fi
 
 if ps -u "$SERVER_USER" &>/dev/null ; then