feat: validate plan ID and repo ID

internal/config/stringutil/stringutil.go

@@ -2,7 +2,15 @@ package stringutil
 
 import "regexp"
 
+var (
+	sanitizeIDRegex = regexp.MustCompile(`[^a-zA-Z0-9_\-\.]+`) // matches invalid characters in an ID
+	idRegex         = regexp.MustCompile(`[a-zA-Z0-9_\-\.]*`)  // matches a valid ID (including empty string)
+)
+
 func SanitizeID(id string) string {
-	reg := regexp.MustCompile(`[^a-zA-Z0-9_\-\.]+`)
-	return reg.ReplaceAllString(id, "_")
+	return sanitizeIDRegex.ReplaceAllString(id, "_")
+}
+
+func ValidateID(id string) bool {
+	return idRegex.MatchString(id)
 }