Implement a janitor service to manage ident update

[TristanCacqueray]

To update ident we currently use the crawler-legacy container to run a one shot command. Instead we could use an extra service to watch for ident change and apply the difference automatically. The service could also be used to apply batch job such as curating the audit index (#453).

• [ ] Store the current config in the audit index.
• [ ] When the configuration change, applies the diff with the last one from the audit, then update the audit index.
• [ ] Remove the command from the crawler-legacy