Created auth interceptor for use with Angular's HttpClient

[Blackbaud-PaulCrowder]

The implementation contains a workaround for passing additional context to the interceptor since Angualr doesn't currently support it. Here is an issue describing the problem: angular/angular#18155

[codecov-io]

Codecov Report

Merging #11 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #11   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           2      5    +3     
  Lines          47    103   +56     
  Branches       10     24   +14     
=====================================
+ Hits           47    103   +56

Impacted Files	Coverage Δ
...ublic/modules/auth-http-client/auth-interceptor.ts	100% <100%> (ø)
...odules/auth-http-client/auth-interceptor-params.ts	100% <100%> (ø)
...pp/public/modules/auth-http-client/auth-options.ts	100% <100%> (ø)

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[Blackbaud-SteveBrush]

Tested. Works great; code looks great.

[Blackbaud-SteveBrush]

@blackbaud-johnly We'll need a documentation task for this, please.

[blackbaud-johnly]

Created https://github.com/blackbaud/skyux2/issues/2187 to document this.