add base uri to http client created by integration factory

[galvani]

Q	A
New feature/enhancement? (use the a.x branch)	[ ]

Description:

If you initiate an HTTP client through the integration's OAUTH HttpFactory, there is no way to set a base_uri, so every request needs the full URL in request. This allows the Credentials used to factor the client to set the base_uri config parameter.

Steps to test this PR:

As a developer you need to implement new HTTP client and try

Implemented test makes use of deprecated function, which won't be deprecated.
guzzle/guzzle#3114 (comment)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.78%. Comparing base (51146d1) to head (f67e554).
Report is 1 commits behind head on 5.x.

❗ Current head f67e554 differs from pull request most recent head 05e213e. Consider uploading reports for the commit 05e213e to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##                5.x   #12760      +/-   ##
============================================
- Coverage     61.39%   58.78%   -2.62%     
+ Complexity    34024    33161     -863     
============================================
  Files          2238     2198      -40     
  Lines        101686    99244    -2442     
============================================
- Hits          62432    58338    -4094     
- Misses        39254    40906    +1652     

Files	Coverage Δ
...le/Auth/Provider/Oauth2ThreeLegged/HttpFactory.php	98.38% <100.00%> (+0.08%)	⬆️

... and 486 files with indirect coverage changes

[kuzmany]

Yes, make sense

[nick-vanpraet]

code looks clean