fix(settings): read PEM files but b64 env vars

- Extract base64 data from PEM files and secret files
- Environment variables are not PEM encoded and only the base64 data
- Affects OpenVPN certificate, key and encrypted key

internal/configuration/sources/env/helpers.go

@@ -1,7 +1,6 @@
 package env
 
 import (
-	"encoding/base64"
 	"fmt"
 	"os"
 	"strconv"
@@ -133,15 +132,6 @@ func lowerAndSplit(csv string) (values []string) {
 	return strings.Split(csv, ",")
 }
 
-func decodeBase64(b64String string) (decoded string, err error) {
-	b, err := base64.StdEncoding.DecodeString(b64String)
-	if err != nil {
-		return "", fmt.Errorf("cannot decode base64 string %q: %w",
-			b64String, err)
-	}
-	return string(b), nil
-}
-
 func unsetEnvKeys(envKeys []string, err error) (newErr error) {
 	newErr = err
 	for _, envKey := range envKeys {