Fleet UI: Open a modal moves updates active element to modal elements

[RachelElysia]

Issue

Part of #23266

Description

• Better keyboard accessibility for modals
  • When opening a modal, the keyboard active element is now within the modal and not back on the main page
  • Figured out how to make the focusable element go back to the original element when closing the modal :)
  • Works on current FF, Chrome, not Safari

Screenrecording

Screen.Recording.2024-12-26.at.2.30.18.PM.mov

QA

• When opening any modal with a keyboard in Chrome or FF, you now can to tab through the modal immediately as it moves the focus to an element within the modal
• When exiting the modal with keyboard, make the focusable element go back to the original element that was focused before opening the modal

Checklist for submitter

If some of the following don't apply, delete the relevant line.

• Manual QA for all new/changed functionality

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 3 lines in your changes missing coverage. Please review.

Project coverage is 63.79%. Comparing base (ec43ee2) to head (e6d173d).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
frontend/components/Modal/Modal.tsx	88.88%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #25020   +/-   ##
=======================================
  Coverage   63.78%   63.79%           
=======================================
  Files        1610     1610           
  Lines      153230   153257   +27     
  Branches     4012     4020    +8     
=======================================
+ Hits        97743    97767   +24     
- Misses      47694    47697    +3     
  Partials     7793     7793           

Flag	Coverage Δ
frontend	53.51% <88.88%> (+0.07%)	⬆️

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[RachelElysia]

Converting to draft as I want to test as many modals as possible before review.