feat(css): Add large breakpoint flex-end alignment

What does this MR do?

While working on this bug I realised we don't have an lg variant for flex-end.

This MR adds that variant so I can use it to resolve the visual bug in GitLab 😄

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• [-] If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• [-] If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• [-] If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • [-] GitLab: mr_url
  • [-] CustomersDot: mr_url
  • [-] Status Page: mr_url
• [-] Added the ~"component:*" label(s) if applicable.

Security

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• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] Security reports checked/validated by a reviewer from the AppSec team