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

app/server_test.go

@@ -34,10 +34,16 @@ func TestStartServerSuccess(t *testing.T) {
 
 func TestStartServerRateLimiterCriticalError(t *testing.T) {
 	// Attempt to use Rate Limiter with an invalid config
-	ms, err := config.NewMemoryStore(true)
+	ms, err := config.NewMemoryStoreWithOptions(&config.MemoryStoreOptions{
+		SkipValidation: true,
+	})
+	require.NoError(t, err)
+
+	config := ms.Get()
+	*config.RateLimitSettings.Enable = true
+	*config.RateLimitSettings.MaxBurst = -100
+	_, err = ms.Set(config)
 	require.NoError(t, err)
-	*ms.Config.RateLimitSettings.Enable = true
-	*ms.Config.RateLimitSettings.MaxBurst = -100
 
 	s, err := NewServer(ConfigStore(ms))
 	require.NoError(t, err)