Add justify-self utility

[oooFreaKooo]

Description

This PR adds support for the justify-self CSS property to Bootstrap’s utilities.
It introduces responsive classes for controlling an element’s alignment inside a grid.

Example:

<div class="d-grid">
  <div class="justify-self-start">Left</div>
  <div class="justify-self-start justify-self-lg-end">Left on mobile, Right on desktop</div>
  <div class="justify-self-center">Center</div>
  <div class="justify-self-end justify-self-lg-center">Right on mobile, Center on desktop</div>
</div>

Motivation & Context

• Related issue: Where is justify-self #25673
• The justify-self property is now widely supported: [MDN docs](https://developer.mozilla.org/en-US/docs/Web/CSS/justify-self).
• Currently, Bootstrap provides align-self utilities but not justify-self.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/main/.github/CONTRIBUTING.md)
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

https://deploy-preview-41734--twbs-bootstrap.netlify.app/docs/5.3/utilities/justify-self/

Related issues

Closes #25673