Replace Bootstrap Button & LoadingButton w/ GitLab UI GlButton in vulnerability_action_buttons.vue

What does this MR do?

Replaces instances of Bootstrap Button & LoadingButton components with GitLab UI GlButton component to improve performance of our application & ensure consistency across the GitLab UI.

Screenshots

Type	Before	After
Zoom

NOTE - the difference in border color was reviewed by our UX counterpart @andyvolpe & signed off on in this comment. The Secondary GlButton component does not support the previous gray border color for the success, info, and warning variants we're using.

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

Issues: #229297 (closed) #229217 (closed)