Add TODO list management
<!--- Please read this! Before opening a new issue, make sure to search for keywords in the issues filtered by the "feature" label: - https://gitlab.com/gitlab-org/cli/-/issues/?label_name%5B%5D=type%3A%3Afeature and verify the issue you're about to submit isn't a duplicate. ---> ### Problem to solve It would be nice to have ability to manage GitLab TODO list from CLI. ### Proposal add `todo` group of commands with `list` and `done` commands. ### Further details One of the examples is CLI shell integration prompting of outstanding items at each login etc. ### Links / references
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