馃殌 Create a new Task work item from Markdown Task
## Follows
- [Show additional meta-data in issue reference in rendered GFM](https://gitlab.com/gitlab-org/gitlab/-/issues/345170)
## Problem
There is no way to create an issue type of `Task` from an existing issue
## Proposal
### Now
Shameless MVC to make this capability general available:
- Expose a button to convert markdown checklist item to Task work item. [See how GitHub handles this](https://gitlab.com/gitlab-org/gitlab/-/issues/2036#note_646045173)
- The `Task` work item is related to the issue (work item of type `Issue`) and is visible in the "linked issues" section of `Issue`
### UX
- In this mockup, the icon is paired with the re-ordering icon, which will be implemented as part of https://gitlab.com/gitlab-org/gitlab/-/issues/15260


### Later
Later on:
- Product planning can migrate Task to be an "official" child on an issue for Premium+ customers.
- Product planning can integrate whatever new relationship management UI they deem necessary into the legacy issue view and new work item detail view.
### Not in scope
- This functionality will only exist on `type === Issue`
- Tasks cannot be created from the general issue creation flow
### Fringe cases to clarify
- If the issue of type `Task` is in an issue and I right-click and select "Copy Link", then enter that URL into the `Linked Issues` in another issue, what happens?
- If we show issue of type `Task` in the issue list, what happens when you click on that particular issue to open it?
## Tier
- ~"GitLab Core" if `Task` is just a related issue.
- `Task` is just a type of Issue and [we've already made the decision](https://gitlab.com/gitlab-org/gitlab/-/issues/323404#note_521563531) that default issue types (can't change type name, can't customize anything, no hierarchy of types) will be in ~"GitLab Core" so we can make types "work by default" for all GitLab Projects.
- ~"group::product planning" can decide how to tier the parent/child stuff. This does expose the need to have issue types support different types of relationships depending on tier.
## Implementation Steps
- [ ] ...engineering task here
epic