Add Docker support for easier deployments

[alfonsrv]

[simo5]

@alfonsrv can you please apply DCO and rebase on main ?

[alfonsrv]

Hey @simo5, can you check if it's okay now?

I also uppercased realm because I found that Windows clients send the realm as both uppercase and lowercase depending on what part of the system the request originates from. This would otherwise require a configuration that factors in both uppercase and lowercase realms. Alternatively the matching logic of finding the realm could be changed to be case-insensitive.