Apply GitLab UI button styles to buttons in ee/app/views/subscriptions/groups directory

What does this MR do?

Apply GitLab UI button styles to buttons in ee/app/views/subscriptions/groups directory

&3963 (closed)

closes #231126 (closed)

Diff in computed CSS can be seen here: https://www.diffchecker.com/5GH96JBJ

Screenshots

Before	After

Steps to test locally

Probably need to update the branch locally.

Hit http://localhost:3000/-/subscriptions/groups/[GROUP-NAME]/edit

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #231126 (closed)