make config dir configurable

Signed-off-by: Jörn Friedrich Dreyer <jfd@butonic.de>

ocis-pkg/config/helpers.go

@@ -31,14 +31,23 @@ var (
 func DefaultConfigSources(filename string, drivers []string) []string {
 	var sources []string
 
-	for i := range defaultLocations {
-		dirFS := os.DirFS(defaultLocations[i])
+	locations := []string{}
+	if os.Getenv("OCIS_CONFIG_DIR") != "" {
+		// only use the configured config dir
+		locations = append(locations, os.Getenv("OCIS_CONFIG_DIR"))
+	} else {
+		// merge config from all default locations
+		locations = append(locations, defaultLocations...)
+	}
+
+	for i := range locations {
+		dirFS := os.DirFS(locations[i])
 		pattern := filename + ".*"
 		matched, _ := fs.Glob(dirFS, pattern)
 		if len(matched) > 0 {
 			// prepend path to results
 			for j := 0; j < len(matched); j++ {
-				matched[j] = filepath.Join(defaultLocations[i], matched[j])
+				matched[j] = filepath.Join(locations[i], matched[j])
 			}
 		}
 		sources = append(sources, matched...)