/troubleshoot slash command on GitLab Duo Chat
## Context
This epic houses individual issues to implement an `/troubleshoot` slash command on GitLab Duo Chat.
## Behavior
Slash command behavior is detailed in [Pajamas documentation](https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/3909). (At the time of writing, the MR is not yet merged)
* `/troubleshoot` should work without arguments on pages that support it
* On pages that do not support `/troubleshoot`, the user is prompted to attach a URL or [GitLab specific reference](https://docs.gitlab.com/ee/user/markdown.html#gitlab-specific-references)
epic