MM-14143 config cleanup final (#10374)

* TestGetLicenseFileFromDisk: avoid using fileutils.FindConfigFile

* config: abstract config-related file access, extend memory store

* simplify config validate to avoid file knowledge

* fix relative file tests

* cluster: fix ConfigChanged event

The old and new configurations were swapped when notifying the enterprise code of configuration changes, creating needless instability in propagating config updates across a cluster.

* config/database: ignore duplicates

* test cleanup

* remove unnecessary Save() in test

config/store_test.go

@@ -2,6 +2,9 @@ package config_test
 
 import (
 	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/mattermost/mattermost-server/config"
@@ -11,6 +14,14 @@ import (
 func TestNewStore(t *testing.T) {
 	sqlSettings := mainHelper.GetSqlSettings()
 
+	tempDir, err := ioutil.TempDir("", "TestNewStore")
+	require.NoError(t, err)
+
+	err = os.Chdir(tempDir)
+	require.NoError(t, err)
+
+	require.NoError(t, os.Mkdir(filepath.Join(tempDir, "config"), 0700))
+
 	t.Run("database dsn", func(t *testing.T) {
 		ds, err := config.NewStore(fmt.Sprintf("%s://%s", *sqlSettings.DriverName, *sqlSettings.DataSource), false)
 		require.NoError(t, err)