feat: enable editing of any plugin config

[Regaez]

Closes #22

• [x] Create PluginHandler class to simplify finding plugin
• [x] Create new PATCH /api/plugins/{id} endpoint
• [x] Create handler for updating plugin config
• [x] Adjust plugin config to disable all endpoints by default and add user override config
• [x] Write tests to cover new functionality
• [x] Document new endpoint in API specification
• [x] Update postman collection

[Regaez]

👍