Jira Connect App: Move user link code from HAML to Vue

As part of #339428 (closed), much of the Jira Connect App UI logic will be shifted from HAML to Vue.

The code for the user link (in the top-right of the Jira Connect App window) still needs to be moved

Code to move: https://gitlab.com/gitlab-org/gitlab/blob/ccaaca1dc8f955f024f13b0354fae06e88e0761b/app/views/jira_connect/subscriptions/index.html.haml#L5

Possible approach

1. Add relevant data to jira_connect_app_data (the method that generates the data attribute used by Vue).
2. Create and use Vue component