Allow users can edit external exercise if having update permission

[KoWeiJAC]

What's included?

closes #2254

The problem here is that we don't want all users to be able to publish all exercises; we want Ops senior managers (but not Ops team members) to be able to publish all exercises, but we want 2/3 users to be able to publish only external exercises without having to gain approval.
we would only want Adela and Gemma (Operations Team Member) plus Ops Senior Leaders to publish external exercises.

Who should test?

✅ Product owner
✅ Developers
✅ UTG

Related permissions

Test as user in Operations Team Member group, without Can publish an exercise as live permission, but has following permissions:

• Can read exercises
• Can create exercises
• Can update exercises

How to test?

• Change the user role of log-in account to Operations Team Member which should be without Can publish an exercise as live permission.
• Go to external exercises of the preview link: https://jac-admin-develop--pr2370-feat-2254-remove-ext-rkhkcll3.web.app/exercise/h5NnKG22oWc6qT12D2VC/externals, it should appear Publish on website or Remove From Apply Site button, and the actions of these buttons should reflect on the apply site: https://apply-develop.judicialappointments.digital/vacancies .
• Go to internal exercises of the preview link: https://jac-admin-develop--pr2370-feat-2254-remove-ext-rkhkcll3.web.app/exercise/77MKqzFIG5imN8ttB6Vl/details/overview, it shouldn't appear publish button.

Risk - how likely is this to impact other areas?

🟢 No risk - this is a self-contained piece of work

Additional context

Include screen grabs, video demo, notes etc.

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PREVIEW:DEVELOP
can be OFF, DEVELOP or STAGING

[github-actions]

Visit the preview URL for this PR (updated for commit 6a52d13):

https://jac-admin-develop--pr2370-feat-2254-remove-ext-rkhkcll3.web.app

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[nickaddy]

@KoWeiJAC Happy to approve. Could you make sure the 'rules' are clearly laid out in the PR pls?