This MR makes several major tweaks to the codebase. Primarily it adjusts
the setup steps for the application so that rather than providing just
the project ID in the `.gitlab.nvim` file, users can also provide a
vareity of other settings, such as auth_token, base_branch, and so
forth. This is to make the project more extensible in the future.
This MR also fixes a variety of issues with error handling in the code,
primarily in the request/response model between the Lua jobs and the
Golang server.
BREAKING CHANGE: Modifies `.gitlab.nvim` and setup steps
