Add displayOnly config option

[spencersablan]

Adding the new displayOnly config option which will allow merchants to show only vaultable buttons.

paypal.Buttons({
    displayOnly: ["vaultable"]
})

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (aa10eff) 100.00% compared to head (0c96c9d) 100.00%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #431   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines          261       261           
  Branches        47        47           
=========================================
  Hits           261       261           

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