Add admin crud UI

[murny]

This PR builds off of #625 to add a CRUD UI for our new Admins resource

Most of this code was largely generated off the scaffold generator from ComfortableMexicanSofa.

In the CMS admin area, you will now have Admins and Log out links:

Clicking on the Admins link will take you to a full CRUD (create, read (index/show), update, delete) of the Admins resource.

Index:

Show:

Update:

New:

And you can delete users.

This is obviously very basic and simple, but should give you a foundation to add upon this and make it better.

You could later expand on this and include ability to invite admins (and remove the "new" admins stuff), ability to disable admins, add audit trail information and so forth (can take inspiration from Jupiter maybe for some of this, but by using Devise you have lots of guides/examples/solutions from the community you could adopt).

For the time being, this gives you an easy way to:

• add new admins (not great honestly because you have to create an account for them and then message/email them their email/password, which they would have to reset themselves etc. Which it is nice to quickly add a way to invite users instead, or look into Ualberta Login integration via SAML)
• Can view and manage admins
• Can remove admins

Improvements:

• Add tests for these new screens (comfy generator added controller tests but these probably need to be fixed and refactored to work, but might be a great starting point)
• Make UI more petterier/functional
• Some forms might not be ideal (Edit form I believe is useless unless you know the users password, but this could be fixed/tweaked)

Future work:

• Most of the suggestions in Add authentication via devise #625 are valid here too (Omniauth-SAML/invitation user provision flow/etc)
• Improve the CRUD screens to our requirements
• Natasha wanted the ability to hide CMS pages from others, will need to implement something based off https://github.com/comfy/comfortable-mexican-sofa/wiki/HowTo:-Password-protecting-pages. (This is done now in Add ability to password protect certain pages #636 )

[murny]

Scaffold uses .page helper and assumes pagination. Comfy mexican suggests either Will Paginate or Kaminari gems:

https://github.com/comfy/comfortable-mexican-sofa?tab=readme-ov-file#dependencies

Pagination is handled by kaminari or will_paginate. Please add one of those to your Gemfile.

So brought in Kaminari just because we use it in Jupiter (no strong opinions otherwise)

[murny]

Mainly all this code below is from the scaffold generator: https://github.com/comfy/comfortable-mexican-sofa/wiki/HowTo:-Reusing-Admin-Area