Allow monitoring Token Quota limits on every M2M authentication call

[kailash-b]

Changes

• A new property Headers will now be exposed as part of the AccessTokenResponse.
• This property will contain all the raw headers returned as part of the http response.
• Extension methods on Headers property will allow users to parse the raw response headers into easily understandable models. (shown in examples.md)
• Augmented the RateLimitException with more details to distinguish if the rate limiting was due to token quota breach or was due to generic limiting rules set.

References 📚

• SDK-5883

Testing

• Added unit and integration test cases for the newly added response header parsing, extension methods, rate-limit exception.

• This change adds unit test coverage

• This change adds integration test coverage

• This change has been tested on the latest version of the platform/language or why not

Checklist

• I have read the Auth0 general contribution guidelines

• I have read the Auth0 Code of Conduct

• All existing and new tests complete without errors

[codecov]

Codecov Report

Attention: Patch coverage is 96.90722% with 3 lines in your changes missing coverage. Please review.

Project coverage is 75.00%. Comparing base (42bf3b6) to head (65ffe24).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Auth0.Core/Exceptions/RateLimit.cs	84.61%	0 Missing and 2 partials ⚠️
...nticationApi/HttpClientAuthenticationConnection.cs	91.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #808      +/-   ##
==========================================
+ Coverage   74.62%   75.00%   +0.38%     
==========================================
  Files         442      444       +2     
  Lines        5714     5805      +91     
  Branches      350      363      +13     
==========================================
+ Hits         4264     4354      +90     
+ Misses       1296     1295       -1     
- Partials      154      156       +2     

Flag	Coverage Δ
authIntTests	30.88% <48.45%> (+0.31%)	⬆️
mgmtIntTests	57.03% <38.14%> (-0.34%)	⬇️
unittests	5.96% <97.61%> (+1.70%)	⬆️

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