Allow disabling sign ups on Bencher Self-Hosted

[Xenira]

I would like to disable sign up on my self hosted instance via config option.

• Remove the button and form in the UI
• Disable api endpoint

[epompeii]

Hey @Xenira, I agree this would be a very useful feature. This is something I have considered adding. However, it would be a Bencher Plus feature.

If this is still something that you'd be interested in, please let me know.