FE: Work Items - Create/edit flows: Apply template
## Proposal
Add an "Apply template" action to the description field, similar to legacy issues. When selecting a template, the template text is used in the description. If the description has been edited in any way, the user must confirm the action as it will delete their prior edits.
<details>
<summary>Previous Proposal — Templates within editor</summary>
## Proposal
* As part of the work to define the work items create/edit flows, we are proposing an integration of the description template selection in the editor.
* This proposed change is only for the work items creation/edit flow. We can leave the description template selection where it is for other legacy types of items.
* [Link to commentary on proposal.](https://gitlab.com/gitlab-org/gitlab/-/issues/418133/designs/Create.png#note_1609643482 "Create.png")
</details>
## Acceptance
- [ ] I can select and apply a template when creating a new work item.
- [ ] I can select and apply a template when editing an existing work item.
## What is this work part of
* This work is part of updates to the [work item detail page](https://gitlab.com/groups/gitlab-org/-/epics/10814#iteration-1b-two-column-layout-sidebar-attributes-and-edit-experience "[UX] Detail pages for Plan related Work Items") to set the stage for epics/issue migrations.
* This is also part of an idea to create a one-stop shop for all work item-type creations. For example, the experience of creating a Requirements, Epic, OKR, or an Issue should all begin with the same form. More info on this [in the Problem part of this Issue](https://gitlab.com/gitlab-org/gitlab/-/issues/418133/ "[UX] Create flow for planning objects").
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