Add AppSecret to Facebook Auth

[dplewis]

Closes: #5448

Copied existing code from FacebookAcountKit

[codecov]

Codecov Report

Merging #5695 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #5695      +/-   ##
==========================================
+ Coverage   94.16%   94.21%   +0.05%     
==========================================
  Files         130      130              
  Lines        9264     9270       +6     
==========================================
+ Hits         8723     8734      +11     
+ Misses        541      536       -5

Impacted Files	Coverage Δ
src/Adapters/Auth/facebook.js	86.95% <100%> (+10.48%)	⬆️
...dapters/Storage/Postgres/PostgresStorageAdapter.js	96.9% <0%> (+0.08%)	⬆️
src/Adapters/Storage/Mongo/MongoStorageAdapter.js	92.45% <0%> (+0.72%)	⬆️

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