Configuration: Fix env var override of sections containing hyphen (#25178)

Fixes so that ini-sections containing hyphen is replaced with
underscore. Fixes an issue with backend plugin settings.

Ref grafana/grafana-image-renderer#147

(cherry picked from commit 34d5ffa562)

pkg/setting/setting.go

@@ -373,6 +373,7 @@ func applyEnvVariableOverrides(file *ini.File) error {
 
 func envKey(sectionName string, keyName string) string {
 	sN := strings.ToUpper(strings.Replace(sectionName, ".", "_", -1))
+	sN = strings.Replace(sN, "-", "_", -1)
 	kN := strings.ToUpper(strings.Replace(keyName, ".", "_", -1))
 	envKey := fmt.Sprintf("GF_%s_%s", sN, kN)
 	return envKey