Description

add mdx file for Dialog/Modal component. demonstrate how to use header, content and action buttons

Why

Please delete options that are not relevant.

[x] I have followed the contributing guidelines
[ ] I have performed IP checks for added or updated 3rd party libraries
[ ] I have created and linked IP issues or requested their creation by a committer
[x] I have performed a self-review of my own code
[x] I have successfully tested my changes locally
[ ] I have added tests that prove my changes work
[ ] I have checked that new and existing tests pass locally with my changes
[ ] I have commented my code, particularly in hard-to-understand areas