Feature: Configure callback

[staff0rd]

I'd like to attempt to make the hardcoded callback url (http://localhost:3000) for openid implicit to be configurable. Is this a feature you'd be interested in merging were I to open a PR?

At the very least, I'd expect to be able to use something like --callback http://localhost:8653/whatever/path or similar via CLI option and the http server to respect this.

[AnWeber]

The change would also affect the VSCode extension. Therefore, when starting the server, it would be necessary to check whether a server has already been opened on this port and to reuse it if necessary. This makes it necessary to manage the servers that have been started.
To customize the path, the logic for recognizing the callback call must be adjusted.

I actually don't mind features that extend functionality. However, backwards compatibility should always be taken into account (if possible).

[AnWeber]

The pull request I have just published with the new version