SDK: add sign-in flow

[blattersturm]

There's a few enhancements that could be enabled by the SDK having a concept of a currently signed-in user:

1. Automatically using a license key selected in the built server output (requires svkey2 changes)
2. Automatically setting a linked admin in txAdmin, once we add bundling/auto-configuration
3. Providing a valid (albeit faked) fivem: identifier for the local user in the dev server
4. Setting the author field in a new resource

This should be easy to implement as idms2 has support for device code flow already since moving to node-oidc-provider, assuming the implementation is using a similar node flow (in the backend) instead of trying to be browser-only.

With device flow, the browser will be opened (with a pre-filled linking code?) and then consent will not need any actual redirect URL but instead will see the client app poll for the consent flow to complete in a standardized way.