[web] Add success variant to Button component

Summary: Added success variant to button component based on atuls previous comments.

Test Plan:
Please view the attached screenshots to see the before and after to see the changes i implemented:

Before: (the only color the button had)

After:
success and success hover example:

disabled example:

Reviewers: atul

Reviewed By: atul

Subscribers: ashoat, tomek, atul, abosh

Differential Revision: https://phab.comm.dev/D5088