Added support for requests session

[infohash]

1. requests.Session allows session persistence across multiple requests.
2. Custom Transport Adapters

Transport Adapters provide a mechanism to define interaction methods for an HTTP service. In particular, they allow you to apply per-service configuration.

Requests ships with a single Transport Adapter, the HTTPAdapter. This adapter provides the default Requests interaction with HTTP and HTTPS using the powerful urllib3 library. Whenever a Requests Session is initialized, one of these is attached to the Session object for HTTP, and one for HTTPS.

Requests enables users to create and use their own Transport Adapters that provide specific functionality. Once created, a Transport Adapter can be mounted to a Session object, along with an indication of which web services it should apply to.

In some enterprise services, there can be a requirement of using custom transport adapters. Allowing a user to directly pass requests.Session instance will satisfy such requirements and flexibility to manage and configure http requests

[infohash]

SKIPPED:  py36: InterpreterNotFound: python3.6
SKIPPED:  py37: InterpreterNotFound: python3.7
  py38: commands succeeded
  docs: commands succeeded
ERROR:   quality: commands failed
Error: Process completed with exit code 1.

[infohash]

@tpazderka After merging upstream/python-versions, checks here are failing while #805 has passed all checks.

SKIPPED:  py37: InterpreterNotFound: python3.7
  py38: commands succeeded
SKIPPED:  py39: InterpreterNotFound: python3.9
SKIPPED:  py310: InterpreterNotFound: python3.10
  docs: commands succeeded
ERROR:   quality: commands failed
Error: Process completed with exit code 1.

[tpazderka]

You have errors in typing, you can run tox -equality to see that.

[infohash]

Fixed and ready to be merged. When will be the expected date of release?

[codecov-commenter]

Codecov Report

Merging #806 (cf4ec39) into master (1e7ed6f) will increase coverage by 0.00%.
The diff coverage is 71.42%.

@@           Coverage Diff           @@
##           master     #806   +/-   ##
=======================================
  Coverage   63.75%   63.75%           
=======================================
  Files          64       64           
  Lines       11850    11856    +6     
  Branches     2410     2411    +1     
=======================================
+ Hits         7555     7559    +4     
- Misses       3698     3699    +1     
- Partials      597      598    +1     

Impacted Files	Coverage Δ
src/oic/oauth2/base.py	54.79% <33.33%> (-1.55%)	⬇️
src/oic/utils/settings.py	87.87% <100.00%> (+1.67%)	⬆️

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