feat: add position prop to modal

[amanabiy]

Description

This PR adds a prop position to the modal to allow builders choose position of center or top. This is a follow up to this pull request which adds x-large and xx-large.

Related links, issue #, if available: gfq0AFhyrah9

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.42%. Comparing base (12d64a9) to head (c29e674).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4243   +/-   ##
=======================================
  Coverage   97.42%   97.42%           
=======================================
  Files         892      892           
  Lines       26116    26117    +1     
  Branches     9437     9438    +1     
=======================================
+ Hits        25444    25445    +1     
  Misses        666      666           
  Partials        6        6           

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[gethinwebster]

I think "focus" is not quite the right word as it might suggest keyboard focus

Suggested change

	* vertical repositioning that causes users to lose focus.
	* vertical repositioning that can cause users to lose context.

[gethinwebster]

will both of these pages be added to visual regression tests?

[amanabiy]

Yes, they will be used in visual regression test.