Update buttons to use Pajamas::ButtonComponent

This merge request updates the buttons in the following files to use Pajamas::ButtonComponent.

File	Issue
app/views/projects/issues/service_desk/_nav_btns.html.haml	#417834 (closed)

I used the instructions provided in this issue, but feedback is always welcome!

Please note: I opted not to update dropdown triggers in this file as they'll be handled in &1059 instead.

Screenshots

Before	After

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