update loading button to use tooltip directive

What does this MR do?

In the course of working on #25351 (closed), I discovered the stop button in the deployment footer was not showing its tooltip on hover. That's because the loading button did not have the tooltip directive. This MR updates that. There is also an issue to update to gl-button (#33362 (closed)), but that is being held up because of a custom classes bug (gitlab-ui#458 (closed)).

This update will allow me to continue on #25351 (closed) with functional tooltips and consistent buttons.

Screenshots

before	after

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Style guides

Performance 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