Add setting to stop displaying popup about missing GitLab token

Summary

Every time VSCode starts, Gitlab Workflow asks for my GitLab token. I would like this extension to have a setting to stop asking me about it. I will provide the token when I want to provide the token.

Steps to reproduce

Open VSCode without having a token to give the extension.

What is the current bug behavior?

Constant pestering in popup form

What is the expected correct behavior?

Don't pester me about a token