Improve install code to avoid low-level mistakes. (#17779)

* Improve install code to avoid low-level mistakes.

If a user tries to do a re-install in a Gitea database, they gets a warning and double check.
When Gitea runs, it never create empty app.ini automatically.

Also some small (related) refactoring:

* Refactor db.InitEngine related logic make it more clean (especially for the install code)
* Move some i18n strings out from setting.go to make the setting.go can be easily maintained.
* Show errors in CLI code if an incorrect app.ini is used.
* APP_DATA_PATH is created when installing, and checked when starting (no empty directory is created any more).

cmd/cmd.go

@@ -16,6 +16,7 @@ import (
 	"syscall"
 
 	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/util"
 
@@ -57,15 +58,17 @@ func confirm() (bool, error) {
 }
 
 func initDB(ctx context.Context) error {
-	return initDBDisableConsole(ctx, false)
-}
-
-func initDBDisableConsole(ctx context.Context, disableConsole bool) error {
-	setting.NewContext()
+	setting.LoadFromExisting()
 	setting.InitDBConfig()
-	setting.NewXORMLogService(disableConsole)
+	setting.NewXORMLogService(false)
+
+	if setting.Database.Type == "" {
+		log.Fatal(`Database settings are missing from the configuration file: %q.
+Ensure you are running in the correct environment or set the correct configuration file with -c.
+If this is the intended configuration file complete the [database] section.`, setting.CustomConf)
+	}
 	if err := db.InitEngine(ctx); err != nil {
-		return fmt.Errorf("models.SetEngine: %v", err)
+		return fmt.Errorf("unable to initialise the database using the configuration in %q. Error: %v", setting.CustomConf, err)
 	}
 	return nil
 }