fix: supporting new cp hook to display provider buttons

[nateiler]

@dsmrt Let's review this; this should use the upcoming hook for our provider buttons.

I remove some of the obvious legacy login template code, but there may be stuff that I missed.

[dsmrt]

Button are looking good

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 81.72%. Comparing base (c22f57f) to head (fffe82f).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Saml.php	60.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #227      +/-   ##
============================================
- Coverage     82.33%   81.72%   -0.62%     
+ Complexity      171      170       -1     
============================================
  Files            16       16              
  Lines           651      651              
============================================
- Hits            536      532       -4     
- Misses          115      119       +4     

Files with missing lines	Coverage Δ
src/Saml.php	91.17% <60.00%> (-5.89%)	⬇️

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[dsmrt]

Bonus!! These get added to the elevated session login too!