FE: Work Items - Add/Resolve Todo
## Summary This is the ~frontend issue for the requirements found in https://gitlab.com/groups/gitlab-org/-/epics/9750. Please find UX specifications below. ## UX Add `todo` button aligned with action menu, using `tertiary` category, `confirm` variant when todo is present. See [prototype](https://www.figma.com/proto/VIBzRhxI3Bq2EfcXUrQW6h/Work-item%3A-To-dos?page-id=0%3A1&node-id=17%3A155999&viewport=-924%2C503%2C0.38&scaling=min-zoom&starting-point-node-id=17%3A155999&show-proto-sidebar=1).
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