Add 'hsts' as config option

src/invidious/helpers/helpers.cr

@@ -128,6 +128,7 @@ user: String,
     check_tables:      {type: Bool, default: false},                 # Check table integrity, automatically try to add any missing columns, create tables, etc.
     cache_annotations: {type: Bool, default: false},                 # Cache annotations requested from IA, will not cache empty annotations or annotations that only contain cards
     banner:            {type: String?, default: nil},                # Optional banner to be displayed along top of page for announcements, etc.
+    hsts:              {type: Bool?, default: true},                 # Enables 'Strict-Transport-Security'. Ensure that `domain` and all subdomains are served securely
   })
 end