Replace HTTP_Request2 with GuzzleHttp

[mrook]

Fixes #1160.

What do you think @siad007 @kenguest ?

[mrook]

Docs still need to be updated.

[kenguest]

looks good to me - unfortunately I'm not currently in a position to test the code but it all seems fine.

[codecov]

Codecov Report

Merging #1288 into master will increase coverage by 0.01%.
The diff coverage is 85.10%.

@@             Coverage Diff              @@
##             master    #1288      +/-   ##
============================================
+ Coverage     51.03%   51.04%   +0.01%     
+ Complexity     9299     9296       -3     
============================================
  Files           479      479              
  Lines         22751    22732      -19     
============================================
- Hits          11610    11603       -7     
+ Misses        11141    11129      -12     

Impacted Files	Coverage Δ	Complexity Δ
...sses/phing/tasks/ext/visualizer/VisualizerTask.php	82.81% <0.00%> (ø)	41.00 <2.00> (ø)
classes/phing/tasks/ext/HttpGetTask.php	82.60% <83.33%> (-11.01%)	20.00 <11.00> (ø)
classes/phing/tasks/ext/HttpRequestTask.php	85.71% <91.66%> (+21.92%)	19.00 <9.00> (-3.00)	⬆️
classes/phing/tasks/ext/HttpTask.php	91.11% <95.00%> (+3.87%)	19.00 <9.00> (ø)

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