Chore: Remove public vars in setting package (#81018)

Removes the public variable setting.SecretKey plus some other ones. 
Introduces some new functions for creating setting.Cfg.

pkg/services/secrets/manager/helpers.go

@@ -26,9 +26,6 @@ func SetupDisabledTestService(tb testing.TB, store secrets.Store) *SecretsServic
 func setupTestService(tb testing.TB, store secrets.Store, features featuremgmt.FeatureToggles) *SecretsService {
 	tb.Helper()
 	defaultKey := "SdlklWklckeLS"
-	if len(setting.SecretKey) > 0 {
-		defaultKey = setting.SecretKey
-	}
 	raw, err := ini.Load([]byte(`
 		[security]
 		secret_key = ` + defaultKey + `

pkg/services/secrets/manager/manager.go

@@ -160,7 +160,7 @@ var b64 = base64.RawStdEncoding
 func (s *SecretsService) Encrypt(ctx context.Context, payload []byte, opt secrets.EncryptionOptions) ([]byte, error) {
 	// Use legacy encryption service if featuremgmt.FlagDisableEnvelopeEncryption toggle is on
 	if s.features.IsEnabled(ctx, featuremgmt.FlagDisableEnvelopeEncryption) {
-		return s.enc.Encrypt(ctx, payload, setting.SecretKey)
+		return s.enc.Encrypt(ctx, payload, s.cfg.SecretKey)
 	}
 
 	var err error