[Time tracking] Update issue spend and estimate times
### Problem to solve This is an extension of the closed issue #934. Looks like it's possible to setup the estimate and time spent on the creation of a ticket. But those options are not present on the `glab issue update` counterpart. Only way is through the web-page or API calls. ### Proposal Same features as using slash-commands on the discussion text-box on an issue page. | Slash | CLI option | Behaviour | | ------ | ------ | ------ | | /spend | --spend | Add given time to current spent time | | /remove_time_spent | --remove-time-spent | Reset spent time | | /estimate | --estimate | Set given time as estimate | | /remove_estimate | --remove-estimate | Reset estimate | ### Further details - This would be useful when working on an issue and report the time spent through the CLI. - Allows scripting with `glab` ### Links / references [Update command options](https://gitlab.com/gitlab-org/cli/-/blob/main/docs/source/issue/update.md)
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