Add a resolve Jira Association button to Merge Requests

Problem to solve

Adding a button which quickly lets the user add a Jira ticket association to an MR would be a nice QOL when a MR is blocked.

Related issues

This issue is part of epic to improve the Jira <> Merge Request experience &4637.

Related issues and suggested order of implementation:

1. Add a project-level toggle to require Jira association in Merge Requests #268294 (closed)
2. Add Jira ticket association requirement to Merge Requests #268292 (closed)
3. This issue
4. Suggest a Jira issue when editing a Merge Request title or description #268296 (closed)

Proposal

If a MR lacks a Jira association:

1. If the feature flag is enabled
2. If the project has Jira integration
3. Add a button Add Jira issue to title or description
4. When the user clicks this, redirect them to the MR edit page.
5. out of scope If possible, auto select or highlight the Jira input field

Implementation

Estimated weight: 2

frontend

• Pass the edit_namespace_project_merge_request_path to the frontend
• Add a Edit merge request button to mr_widget_jira_association_missing.vue (!58658 (merged))
• When clicked, redirect them to the MR edit page