Improve Onboarding and Auth of GitLab Workflow
## Problem to Solve Onboarding in the GitLab Workflow extension is currently quite challenging. Upon initial setup a user is required to specify which GitLab instance they're using and then provide a PAT for authorization. This leads to problems where a project might be used in multiple GitLab instances and detection of the project doesn't work. Users may also not understand how to generate a PAT or need to generate multiple for connecting to multiple instances. ## Proposal We should investigate two changes to the current underlying architecture of the extension: 1. We should to using the configured project remotes as the instance that the extension should talk to. Further details outlined in https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/issues/115#note_410341027 1. We should use OAuth to authorize the extension to each instance with the appropriate permissions. When making the first command we can detect the origin and then prompt the extension to authorize via OAuth.
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