feat: update css variables (MGPFE-2127)

[sonya0504]

Description

Using figma-to-css.mjs update css variables to the newest.
I added two variables to the local file .env: FIGMA_TOKEN and FIGMA_FILE_ID to make it easier to use
Update UiHeading, UiCheckbox and UiIcon with new css variables.

Related Issue

MGPFE-2127
Closes #

Motivation and Context

CL should be in line with Figma

How Has This Been Tested?

Storybook

Screenshots (if appropriate):

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[DanielHajduk98]

LGTM, moving the figma file id to env was long-overdue.