Add Oauth (SAML) authentication support

[mxr576]

No description provided.

[mxr576]

Tests are coming soon.
@cnovak I have just added you as a review to give you a chance to review this code before it gets merged. Let me know if you do not have resources for this.
Also an another question, should OAuth support be part of the alpha release or it should not?

[codecov-io]

Codecov Report

Merging #102 into 2.x-dev will decrease coverage by 5.99%.
The diff coverage is 16.07%.

@@            Coverage Diff             @@
##             2.x-dev     #102   +/-   ##
==========================================
- Coverage      86.42%   80.42%   -6%     
- Complexity       515      562   +47     
==========================================
  Files             69       72    +3     
  Lines           1208     1303   +95     
==========================================
+ Hits            1044     1048    +4     
- Misses           164      255   +91

Impacted Files	Coverage Δ	Complexity Δ
...lugin/Authentication/InMemoryOauthTokenStorage.php	0% <0%> (ø)	21 <21> (?)
...tpClient/Plugin/RetryOauthAuthenticationPlugin.php	0% <0%> (ø)	7 <7> (?)
src/HttpClient/Plugin/Authentication/Oauth.php	0% <0%> (ø)	11 <11> (?)
src/Exception/ApiResponseException.php	69.56% <100%> (+2.89%)	13 <0> (+2)	⬆️
src/HttpClient/Plugin/ResponseHandlerPlugin.php	70.83% <14.28%> (-23.29%)	21 <0> (+4)
src/HttpClient/Client.php	85.88% <91.66%> (-1.33%)	35 <2> (+2)
src/HttpClient/Utility/Journal.php	60% <0%> (+20%)	6% <0%> (ø)	⬇️

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[mxr576]

Merged to the oauth branch.