Add new Gitlab OAuth workflows

User story

As a [user of a Gitlab site not already set up to use the OAuth flow]
I want [to add my site as being able to utilize the OAuth flow]
So that [I don't need to use an API Key anymore]

Tasks

• Restructure the code to make a simple location that can be easily updated by a code novice for updating the site dropdown
• Provide a link to feedback for other local GitHub installs to be available via the OAuth authentication workflow
• Provide instructions on how to update the repository and submit a PR to have a new site added

Acceptance criteria

• I can request to have my Gitlab install added
• I can create a PR to write the code myself to have Gitlab added

Notes