Added functionality for custom url

[DanishKhakwani]

This change will allow users to create custom urls instead of some randomly generated string.

[yudai]

Thank you for the PR. Could you share some use cases with this function? I think putting a proxy in front of gotty can do the same thing. So we need a valid use case to add this function to gotty itself.

[DanishKhakwani]

That's true. I was thinking more in terms of having a single gotty server running which can spawn multiple containers based on the url (for eg. /fedora). But I guess currently we cant have multiple containers running on the same port based on the urls.

[sorenisanerd]

This feature is available in my fork at https://github.com/sorenisanerd/gotty