Allow users to configure their own Headscale instance

[Tpuljak]

Is your feature request related to a problem? Please describe.
Users might have their own headscale instance running and want to reuse it for Daytona as well.

Describe the solution you'd like
Users should be able to configure an existing headscale instance for Daytona.
The solution must allow the Daytona Server to create users and preauth keys for projects.

Additional context
#180

[shuguet]

@Tpuljak why close #180 in favor of this one?
I thought someone was already working on the previous issue?

[Tpuljak]

@shuguet as per #180 (comment), we are unable to reproduce this issue any longer. Since the opening of your issue, a lot of headscale improvements were made that might have resolved it.
If you are still able to reproduce the issue on the latest version of Daytona (v0.40.0) we will reopen it and investigate again.

I decided to open this issue separately since it's an enhancement that we can implement on its own.