Context Plugin doesn't fail gracefully if FileServer is not configured with Context

### Current Behavior

Node-RED fails to start if context plugin fails to load persistent context cache.

The plugin fails because the File Server returns a 401 error if context routes are not loaded (not context configured

### Expected Behavior

Node-RED should not crash even if the file server is not configured to provide persistent context, but should fail to load the persistent context plugin.

Or if the File server is not configured to support the persistent context then it should not be enabled in the settings passed to the launcher.

### Steps To Reproduce

Setup the File Server but without a `context` entry in the yaml file so the context routes do not get loaded

### Environment

- FlowForge version: 1.4
- Node.js version: 16.x
- npm version: 8.x
- Platform/OS: all
- Browser: na