As a user, I can assign test runs even if I can't edit Test Execution issues

Currently, Xray requires the user to have both Edit and Assign permission in the Test Execution in order to assign Test Runs.

Xray should allow a user to assign a Test Run to another user without having Edit permission in the respective Test Execution.

ACs:

• A new project permission should be provided that will allow users to assign Test Runs without being able to edit the Test Execution issues.
• The new project permission should be named "[Xray] Override Assign Test Runs"
• This permission should not be applied to any users by default.
• All Xray screens that allow users to assign Test Runs must be changed to include this new validation. These include:
  • The Test Execution - Tests web panel
  • The Test Run page (assignee field)
  •  Test Plan issue page