Update buttons to use Pajamas::ButtonComponent

What does this MR do and why?

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

File	Issue
app/views/devise/shared/_omniauth_box.html.haml	#417814 (closed)
app/views/clusters/clusters/cloud_providers/_cloud_provider_button.html.haml	#417812 (closed)

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

Screenshots

Before	After

Please note: one of the buttons was removed from this merge request because it is not trivial and require further testing and styling considerations, please see these two comments (1, 2) for more information.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.