Custom Buttons for Login Provider

[alexw92]

Is your feature request related to a problem? Please describe.
I am unsure if this has been addressed already since this issue is quite old #149
But I am using Version 5.0.0 and the Buttons for Social Login are still fixed and dont allow to set e.g. a Material ElevatedButton or so to be used as login button. This could be very useful since provider often change styles of their logos and how their Login UI looks like.
Also not all of the fixed Buttons have "dark" and a "normal" version.

Describe the solution you'd like
Allow Custom Buttons for LoginProviders,